A SIM lock, simlock, network lock or subsidy lock is a capability built into GSM mobile phones by mobile phone manufacturers. Network providers use this capability to restrict the use of these phones to specific countries and network providers. A phone sold without a SIM lock is called a SIM-free or unlocked phone and the purchaser can insert a SIM card of their choice.
- Mobile country code (MCC; e.g., will only work with SIM issued in one country)
- Mobile network code (MNC; e.g., AT&T Mobility, T-Mobile, Vodafone, Bell Mobility etc.)
- Mobile subscriber identification number (MSIN; i.e., only one SIM can be used with the phone)
Additionally, some phones, especially Nokia phones can lock group IDs which are used in voice group call service.
In the United States and other areas, where carriers often offer deeply discounted cell phones in exchange for an exclusive agreement with a carrier, that phone will often be locked so it will not work with another carrier.
Most mobile phones can be unlocked to work with any GSM network provider, but the phone may still display the original branding and may not support features of the new carrier; besides the locking, phones may also have firmware installed on them which is specific to the network provider. For example, a Vodafone or Telstra branded phone in Australia will display the relevant logo and may only support features provided by that network (e.g. Vodafone Live!). This firmware is installed by the service provider and is separate from the locking mechanism. Most phones can be unbranded by reflashing a different firmware version, a procedure recommended for advanced users only.
The reason many network providers SIM lock their phones is that they offer phones at a discount to customers in exchange for a contract to pay for the use of the network for a specified time period, usually between one and three years. This business model allows the company to recoup the cost of the phone over the life of the contract. Such discounts are worth up to several hundred U.S. dollars. If the phones were not locked, users might sign a contract with one company, get the discounted phone, then stop paying the monthly bill (thus breaking the contract) and start using the phone on another network or even sell the phone for a profit. SIM locking curbs this by prohibiting change of network (using a new SIM). SIM locking is very common if subsidized phones are sold with prepaid contracts. It is important to note, however, that the technology associated with the phone must be compatible with the technology being used by the network carrier. A GSM cell phone will only work with a GSM carrier and will not work on a CDMA network provider. Likewise, a CDMA cell phone will only work with a CDMA carrier and will not work on a GSM network provider.
In some jurisdictions, including China, Israel, and Singapore, SIM locking is outright illegal Template:Source required. But in some other countries, many carriers do not provide unlocking codes, and some who do force the consumer to pay a fee. Despite this, unlocking a phone without carrier consent may be legal in some jurisdictions. Additionally, it is often legal for carriers to force SIM locks for certain amounts of time, varying by region.
- 1 Unlocking technology
- 2 Laws and practices
- 2.1 Andorra
- 2.2 Austria
- 2.3 Australia
- 2.4 Belgium
- 2.5 Brazil
- 2.6 Canada
- 2.7 China
- 2.8 Colombia
- 2.9 Chile
- 2.10 Croatia
- 2.11 Denmark
- 2.12 Ecuador
- 2.13 European Union
- 2.14 Finland
- 2.15 France
- 2.16 Germany
- 2.17 Honduras
- 2.18 Hong Kong
- 2.19 India
- 2.20 Israel
- 2.21 Italy
- 2.22 Netherlands
- 2.23 New Zealand
- 2.24 Pakistan
- 2.25 Peru
- 2.26 Portugal
- 2.27 Romania
- 2.28 Singapore
- 2.29 Spain
- 2.30 Sweden
- 2.31 Thailand
- 2.32 United Kingdom
- 2.33 United States
- 3 See also
- 4 References
A handset can be unlocked by entering a code provided by the network operator. Alternative mechanisms include software running on the handset or a computer attached to the handset, hardware devices that connect to the handset or over-the-air by the carrier. Usually the unlock process is permanent. The code required to remove all locks from a phone is referred to as the master code, network code key, or multilock code. There can also be multiple levels of locks placed on the phone by networks, which block the use of other networks' SIM cards. These are usually referred to as "Network" (NCK) or "Service Provider" (SPCK) locks and can be removed using the corresponding unlock codes, which are unique to each phone depending on its IMEI.
Typically, a locked handset will display a message if a restricted SIM is used, requesting the unlock code. On recent phone models running Android software, the phone will display a message saying “SIM network unlock PIN” or “Enter Network Lock Control Key” if network locked. Windows phones will display the message, “This SIM card can only be used on specific networks. Contact your customer service center for the unlock code”. Other handsets may display different messages such as "Enter special code" or "Enter unlocking code," or in some cases the handset will simply display a message stating that it is locked. Once a valid code is entered, the handset will display "Network unlocked” or “Network unlock successful”.
The unlock code is verified by the handset and is generated by the manufacturer, typically by an algorithm such as a one way hash or trapdoor function. Sometimes big telecom providers change the original factory unlock codes as an extra layer of security against unlocking services. For various big brands such as Samsung and Motorola there is no algorithm but just a random code generator where the unlock codes are programmed in the phone itself and then saved in a big database managed by the manufacturer. For the other brands where the unlock codes are still based on algorithms those are based on the IMEI number and the MCC code and have been reverse-engineered, stolen or leaked. Some handsets can be unlocked using software that generates an unlock code from an IMEI number and country and operator details using the algorithm specific to the handset. Other manufacturers have taken a more cautious approach, and embed a random number in the handset's firmware that is retained by the network on whose behalf the lock was applied and the manufacturer. These handsets can still be unlocked by online services that have access to either inside people with the manufacturer or with the telecom networks, or they need to be connected to the computer with a cable where specific software will bypass the security and SIM-unlock the phone. Sometimes this is done by advanced calculations to bypass the security the official way and other times using exploits or overwriting parts of the firmware where the lock status is kept, and often even recover a phone that is bricked or completely damaged in the software sense.
Most handsets have security measures built into their firmware that protects them from repeated attempts to guess the unlock code. After entering more than a certain number of incorrect codes the phone becomes frozen. This is a state where the phone will display a security message that the phone needs service. Older phones could not be used at all anymore at this point, but modern smartphones often keep on working with the original SIM but need extra work to then unlock them the right way. Depending on the brand this "frozen state" can sometimes be resolved both by a special unfreeze code (Samsung) and cable solution and other brands need special cable solutions. In the worst situations one would need a special so-called "JTAG" hardware solution to fix the phone. This is often needed when there is more damage to the software, often including software damage to the "bootloader".
A hardlocked phone is one in which a telecom provider has modified the firmware on the phone to make it impossible to manually enter the unlock codes in any way. The only solution to SIM-unlock such a phone is to change the firmware to a firmware which has not been modified by any telecom provider, a so-called "unbranded firmware".
Handset manufacturers have economic incentives both to strengthen SIM lock security (which placates network providers and enables exclusivity deals) and to weaken it (broadening a handset's appeal to customers who are not interested in the service provider that offers it). Also, making it too difficult to unlock a handset might make it less appealing to network service providers who have a legal obligation to provide unlock codes for certain handsets or in certain countries.
In some cases, a SIM-locked handset is sold at a substantially lower price than an unlocked one, because the service provider expects income through its service. SIM locks are employed on cheaper (pay-as-you-go) handsets, while discounts on more expensive handsets require a subscription that provides guaranteed income. Unlocked handsets have a higher market value, even more so if they are debranded. Debranding involves reflashing or replacing the firmware to remove the operator logo or any limitations or customisations that have been imposed on the handset by the operator, and is usually accomplished with software designed for a particular handset model, however most smart-phones can be debranded and unlocked solely with use of special software.
The main reason to unlock a handset is to be able to use it with a different SIM card. Consumers may wish to continue using their previous provider with a new handset or when traveling abroad they may wish to connect to a foreign network with a prepaid subscription.
Nevertheless, the fundamental principle of GSM and its successors, is open interfaces which encourage competition among multiple vendors. This is the reason a mobile phone is, in fact, a combination of phone and the subscriber identity (SIM). Locking the phone to a network is not much different from having the SIM built into the mobile phone. Network operators in industrialized countries are not bound by law to give the phone unlocking code to subscribers even after the expiry of the contract period. Mobile phones with multiple SIM cards are quite common in India. Most phones sold in the UK are network locked and single SIM but SIM-free phones are available.
A practice known as box breaking is common  in the United Kingdom and other markets. This involves purchasing subsidized handsets (usually pay-as-you-go) from retail stores, unlocking the phones, and then selling them (often abroad) for a higher price than the subsidised retail price. The SIM card that came with the handset is then either thrown away, sold or used elsewhere. This practice is legal in the UK and provides a de facto limit to the extent to which networks are willing to subsidize pay-as-you-go handsets. While the act of box breaking is legal, some businesses are also engaging in illegal activities such as exporting the box-broken phones to other countries, to sell as grey market goods without paying import duties (known as Carousel Fraud) or substituting counterfeit batteries and chargers.
Some companies offer an online unlocking service. This service requires that individuals who wish to unlock a handset provide their IMEI number and sometimes also country and operator details to the company, either via email or a web site. The company will then provide the unlock code for the handset. For some brands such as Nokia and Samsung various services also offer special remote unlock software with instructions where a cable is needed to remove the SIM lock at home. Such companies may email the unlocking code or software which will remotely unlock the device. Some companies also offer unlocking services that require sending IMEI number. Other companies sell unlocking hardware, including devices which fit between the SIM card and the phone to spoof the original network id during registration and devices to read and edit the handset's firmware. The pricing for unlocking a device will vary depending on the network it is locked to and the model itself, as each unlock code is unique to the handset. On average it typically costs around 15 USD depending on model and make, but for newer phones the price can go as high as 50 USD (for Apple unlocking even as high as 150 USD). Some service providers offer unlocking services for their subscribers worldwide.
Unlock code generators
There are online services that will provide an IMEI unlocking service for DCT4 and DCT3 Nokia mobile phones. This method of unlock requires the user to know which carrier the mobile phone is locked to, and also needs to provide an IMEI. Generally, older model Nokia unlock codes are free and instantly retrievable by these services. The unlock codes retrieved must be entered into the mobile phone using the keypad.
For DCT4 and DCT3 Nokia, unlock codes consist of a "#" key, followed by "pw+", 10 (DCT3) or 15 (DCT4) digits, "+", and another number ranging from 1-7, and finally ends with a "#". Depending on the carrier which the phone is locked to, only some codes will work with the mobile phone. Most phones respond to the unlock codes ending in +1# or +7#, however some phones are configured to allow only one of the seven codes to work. The following is an example of a DCT4/DCT3 unlock code:
DCT4 and DCT3 Nokia will only allow a maximum of five unlock attempts using the unlock code method. After five codes have been inputted, the phone will not allow the user to try any more codes (even if it is correct) and will require the owner to try other unlock methods.
There are many free services available online. As smartphones become more advanced, the unlocking of older handsets becomes much more available.
Laws and practices
Many countries listed below have some form of SIM-locking laws specifying the period of SIM locking and the cost of obtaining unlocking codes.
In Andorra, the state-owned communications mobile company Mobiland does not sell SIM-locked phones. As there is no competition, consumers usually buy standard mobile phones that are not locked to any specific carrier.
In Austria, unlocking is allowed at any time by the owner of the device. A lawsuit was decided in favor of a mobile operator who encouraged the unlocking of phones by providing links to free/cheap unlocking services.
T-Mobile Austria charges 150 euro to unlock the iPhone for prepaid subscribers and in contract subscribers. For subscribers who have finished their 2 year iPhone contract, T-Mobile Austria charges 50 euro to unlock the iPhone.
In Australia, carriers can choose whether to SIM/Network Lock handsets or not and usually tend to only SIM/Network lock prepaid handsets. There does not appear to be any regulation or law on SIM locking in Australia.
One law professor, Dale Clapperton, gave a talk stating that bundling iPhone and mobile phone service could be violating the Trade Practices Act. However, no other legal professional or academic has come out in support of this viewpoint. This also doesn't address SIM locking per se, only as applied to subsidised iPhone purchases, and persistence of the lock beyond the contractual period.
Until 2007 Belgium had laws prohibiting bundling, but they were challenged as violating European Directive 2005/29/EC The Unfair Commercial Practices Directive.
On April 23, 2009, the European Court of Justice ruled against Belgium and struck down Belgium's anti-bundling law. The Belgian government was given until May 2009 to change the law, failing which the European Commission would commence proceedings against Belgium.
This leaves China, Singapore and Israel as the only countries in the world that forbid SIM locking and contract/phone bundling outright. Chile initiated a ban as of January 1, 2012.
In Brazil, SIM locks are not prohibited. However, the mobile carrier must inform the consumer of the existence of a SIM lock. Anatel, Brazil's telecom regulator, requires the carrier to unlock free of charge the mobile phone if required by the user. After this regulation most telecom operators started voluntarily unlocking the devices as soon as it was purchased so one could leave the store with an unlocked phone.
On June 3, 2013, the Canadian Radio-television and Telecommunications Commission announced a new wireless code  which encompasses a variety of consumer benefits, including the right of consumers to "have their cellphones unlocked after 90 days, or immediately if they paid for the device in full". The code is effective 2013-12-02.
Under a regulation enacted by the Ministry of Industry and Information Technology, locking phones to a specific carrier is prohibited if other carriers are also using the same type of network technology. Therefore, all phones approved to be sold in China are never locked to begin with regardless of whether the consumer purchased the phone under a contract or not. However, since all three Chinese carriers each uses a different network technology after the adoption of 3G, carriers started to ask phone manufacturers to disable support for network technologies not used by such carrier even if the phone has been originally designed to be capable of supporting those network technologies. Such a move does not result in violation of the ban on phone locking. For example, an iPhone 6 was designed to be capable of supporting LTE FDD, LTE TD, CDMA, and WCDMA technologies but China Mobile reached a deal with Apple to create a special model for China Mobile in addition to the off-contract retail model sold by Apple and third party vendors with the capability to support LTE FDD, CDMA, WCDMA, which are the technologies not used by China Mobile, disabled, effectively making such special contract model incompatible with the 3G and 4G networks of other carriers even though such phones are never locked.
Starting October 1, 2011, all the mobile telephone services providers, must sell to all users unlocked devices and provide free of charge support to unlock previously sold devices. This regulation was ordered to enable mobile number portability and to facilitate the reduction on costs ordered simultaneously.
Chile requires that carriers unlock any device for free starting 1 January 2012. Any company providing mobile telephone services must unlock any device for free. Newly sold phones must be unlocked or be labeled with information about how to get them unlocked. The regulation was put in place in order to implement mobile number portability.
In Croatia, the mobile operator is allowed to SIM lock the device only if it's bought on contract and only for the duration of the contract. After the contract's expiration or termination, the operator must provide the unlock code on the user's request free of charge. For devices bought on a prepaid plan, the operator must provide the unlock code on the user's request after 12 months free of charge.
The carrier can choose to bind contracts up to 6 months from the contract's start. Many of the carriers choose not to lock the phones. Only Hi3G ("3") lock their phones, but can only do so for six months. If the phone needs to be unlocked within the first six months, the carrier can charge DKK 500 (~ €67) for the unlock. After six months, the carrier is obliged by law to unlock the phone free of charge. But the consumer needs to contact the original supplier, and provide the IMEI and original phone number for which the phone was sold.
Countries in the European Union (EU) each have their own legislation on SIM locking, but must comply with the EU Unfair Commercial Practices Directive (Directive 2005/29/EC of 2005). As noted above, this directive has been successfully applied in Belgium to overturn that country's previous ban on bundling phones with contracts. However, carriers in many countries in the EU do not necessarily associate a phone's SIM lock status to the customer's tie-in contract status.
In Finland, carriers are not allowed to sell SIM-locked GSM phones, nor are they allowed to offer tie-in sales on GSM equipment. Under Finnish law, a tie-in sale is defined as selling the equipment for a discounted price contingent on the consumer also acquiring a new service contract from the seller. Under the terms of a provisional exception, valid from 2006 until 2009, tie-in sales were permitted with 3G handsets, and 3G equipment which is purchased under such tie-in sales may be SIM-locked. The SIM lock must be removed free of charge at the conclusion of the tie-in contract, within a maximum duration of 2 years. In 2008, the Finnish government was preparing to extend the exception, and at the same time, was considering reducing the duration of tie-in contracts to one year.
In France, SIM locks are not prohibited. However, the mobile operator must inform the consumer of the existence of a SIM lock, and the subscriber has the right to request that the lock be removed at any time. No later than three months after the subscription of the contract, the mobile operator must "systematically and free of charge" provide the subscriber with a procedure to deactivate the SIM lock. Proposal to shorten the time that operators may charge a fee for removing the SIM lock prior from six-month to the three-month deadline.
In Germany, there does not appear to be any effective law regulating SIM locking. For example, the iPhone was initially offered for sale in Germany exclusively through T-Mobile, and it was locked to T-Mobile's network. They began to provide unlocking codes for that phone after they were sued by Vodafone and a temporary injunction was issued requiring T-Mobile to do so. Vodafone's injunction was later overturned, and the iPhone is again available exclusively locked to T-Mobile. While T-Mobile Germany told the court that they would unlock the iPhone after the contract, they were doing it voluntarily.
As of 2012, usually only prepaid mobile phones are sold with a SIM lock. Phones sold with a contract stipulating monthly payments are not typically locked (as the monthly payments are due no matter what network the phone is used on). Also, most providers will unlock the phone on demand. Usually a fee is charged during the first two years after purchase; afterwards the unlocking is free.
In Honduras, there is a general law applicable to all consumer relations engaged in the national territory and provided by natural or legal persons, public or private. This law is called "Ley de Proteccion al Consumidor" or "Consumer Protection Act of Honduras", approved by Legislative Decree No.24-2008, and it regulates the activities of any goods and services providers stating the principles that they must follow in order to operate in this country.
Article 20 of this law states the prohibitions that sellers are obliged to abide when selling a good or providing a service to people. Paragraph 7 of this article states that it is prohibited to a provider to "place seals, adhesives, duct tapes or analogous mechanisms, which prevent the consumer to make free use of the product, except those mechanisms used by the manufacturer for warranty purposes;".
Even though the existence of this law, local carriers continue to apply SIM restrictions to the phones they sell. For example, the iPhone is sold by Claro in Honduras and is SIM-locked,. which suggests that this general consumer protection law does not prohibit SIM locking of cell phones
In Hong Kong, carriers are not allowed to SIM-lock a phone for the sole purpose of tying customers to their network. But Hong Kong carriers can SIM-lock a phone to protect the handset subsidy, to enforce mobile plan contracts or to protect from theft. After the initial purchase subsidy has been recovered, or the full cost of the equipment has been paid up under a rental or installment agreement, the carrier must provide a detailed procedure for unlocking the equipment free of charge upon request.
SIM locking is not common in India. Initially, each state in India had a different mobile network operator and roaming across states was prohibitive. It was cheaper to change the SIM card than pay high roaming charges. The number of inter-state travelers demanded unlocked phones. Usually, phones and SIM cards are sold separately. Mobile phone manufacturers sell phones directly to customers rather than through network operators. Dual SIM phones are quite common in use, with users choosing to make calls using a cheaper operator suitable for the particular call and time of the day from a Dual SIM phone without even switching it off. This along with other factors, encouraged competition among network operators and brought down the mobile phone call charges in from the initial 32 (US$0.75) in 1996 to 0.50 (US$0.005 approx.) in 2011. The rates still differ from one service provider to another and across different tariff schemes provided by the same operator. Telecom Regulatory Authority of India (TRAI) is the independent regulator of the telecommunications business in India, established to check call rates and resolve all communication related issues and holds the upper hand in fixing call rates.
According to the Arrangements Law passed on December 29, 2010, Israeli carriers are banned from locking handsets sold by them, and are obligated to unlock any handset previously sold at no charge.
Italy has SIM locking laws requiring that carriers must specify the amount of subsidies, and allowing subscribers to obtain unlocking codes after nine months by paying half of the listed subsidies. After 18 months, the SIM lock must be removed.
Dutch mobile carriers have an agreement  with the Netherlands' telecom regulator, OPTA, to establish a code of conduct  with respect to SIM locking — specifically, unlocking fees can be charged within the first 12 months and SIM lock cannot last longer than 12 months.
In a 2002 letter to the Dutch Secretary of State of Economic Affairs, OPTA stated that the telecom regulator has decided to start working on the formalization of the voluntary code of conduct into legislation. However, a 2006 report written by the Dutch Ministry of Economic Affairs, stated that competition in the Dutch mobile market is sufficient and the formalization of the voluntary code of conduct into legislation is not needed. Thus there are no SIM locking laws in the Netherlands.
Locking had occurred in New Zealand only to a limited degree before May 2008 when Vodafone New Zealand announced they would begin locking handsets and charge $50 to unlock them. It is speculated that locking began due to the fact Telecom New Zealand were building their new XT Mobile Network based on UMTS technology, allowing handsets to change networks for the first time as Telecom's existing network (the only other network at that time) was based on CDMA technology. 2degrees were also building their mobile network at this time. After pressure from the Commerce Commission, Vodafone relented on its locking policy and will unlock any locked phones for free once they have been owned for nine months. You can pay to have it unlocked prior to this. Following speculation of a new lower cost, MNVO of Telecom XT details were leaked regarding the Skinny Mobile Network, which would SIM lock handsets.
Ufone has started SIM Locking with the release of its new smart phone named Smart U5 developed by Emitac Services, UAE. U5 comes with SIM locked to Ufone only. No other SIM could be used on U5 smartphone.
A 2006 study sponsored by the Portugal regulator, ANACOM, on handset subsidies and SIM locking concluded that there are no special regulatory concerns on offering subsidized SIM-locked equipment in exchange for signing a contract tying a customer to a particular network. Network providers are allowed to apply SIM locks as they see fit, and they may voluntarily remove them if they choose to do so. In the paper, the author stated that the average unlocking fee charged by Portuguese carriers is 90-100 euros. A recently approved law  requires network operators to unlock a device free of charge if the respective contract has already expired (But they refuse to do so charging at least 10 euros). It also establishes limits to the fees that operators may charge to unlock a device while it is still under contract.
Romanian telecom regulator ANCOM signed a code of conduct with several Romanian carriers providing that as of September 1, 2009 mobile operators selling handsets locked within their own network have to inform clients whether the handset is locked and provide unlocking upon request. It is "self-regulation" by the carriers to prevent the regulator from actually imposing regulations on them. If the handset is not purchased together with other electronic communications services, the mobile telephony operator that sells it will bear the unlocking costs and will not bind the terminal unlocking by the purchase of other services or by the payment of other fees.
If the handset is purchased as part of a promotional package or at a preferential price and the customer requires the unlocking before the expiry of the minimum period provided in the contract for communications services concluded with the operator, the customer will have to pay both the unlocking fee and the penalty for the anticipated unlocking of the handset. The price charged to unlock handsets will not exceed the costs of this operation and operators are obliged to meet unlocking requests within 15 days.
Singapore is the first country that forbids outright SIM locking and contract/phone bundling. Singapore's telecommunications regulator has ruled that the competition clause in mobile carriers' licenses means SIM-locking is not allowed, and has warned at least one operator for selling SIM-locked phones 
In 1998, the Spanish telecom regulator, Comisión del Mercado de las Telecomunicaciones, saw that Spanish mobile carriers already provided unlocking codes voluntarily for a fee within the first 12 months and for free after 12 months, so CMT decided not to put any legal framework in Spain. CMT has not revisited this decision since then, therefore there are no SIM-locking laws in Spain.
In Sweden, carriers are required to unlock handsets after 12 months since purchase. This applies both to on-contract and pay as you go phones. All carriers will charge a fee of 300 SEK (approximately $45) or 350 SEK (approximately $50),depending on carrier, to unlock the handset.
Thailand is also another country that forbids outright SIM locking and as a result, no phones are sold in the market are subsidized by carriers. Up until recently mobile phone manufacturers have their own store fronts and mobile carriers are only the service providers.
In the United Kingdom, mobile phone network providers are not obliged to provide unlocking, even after the end of the contract. Ofcom, UK's telecom regulator, allowed 3 UK to sell a mobile phone with the SIM card permanently superglued to the phone. Most operators offer some form of unlocking service, depending on the state of the contract and the model of phone, but usually for a charge. The full Oftel 2002 SIM-lock position paper specifies that there is no SIM-locking law in the UK; the regulator wants only "consumer awareness". The examples within the position paper are just "examples" of current carrier practices for illustration purposes, but do not reflect any official Oftel regulation. The main networks often agree to unlock handsets for a charge, either at the end of a contract or, for prepaid handsets, after several months. Some Blackberry handsets supplied by Vodafone (e.g., Storm) are examples of a UK carrier not offering unlocking codes. As of April 2011 O2 will unlock any of their pay-monthly phones for free, even if they're still in contract, with the exception of handsets made exclusively for them, such as their Palm devices. Carphone Warehouse, one of the largest UK phone retailers, offers unlocked phones with most PAYG deals.
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One of the two United States GSM carriers, T-Mobile, will unlock handsets for those with active account in good standing for at least 40 days and no unlock code request in the last 90 days. The other, AT&T Mobility, is required to do so upon request (with some exceptions and requirements after ninety days of active service) under the terms of a class action settlement negotiated by Scott A Bursor's class action law firm. Prior to the settlement, AT&T would  usually do so once one has concluded their contract, and in some other situations. AT&T had in the past stated that it would not unlock iPhones under any circumstances, regardless of the legality of doing so, even after customers are out of contract. However, AT&T has since announced that starting April 8, 2012, it will begin unlocking off-contract iPhones, provided that the customer's account is in good standing. AT&T also has an unannounced policy of unlocking iPhones for United States service members who are deployed overseas—even if they are still under contract.
Before carriers began voluntarily providing unlock codes for all phone models, in 2010 the Electronic Frontier Foundation (EFF) successfully convinced the U.S. Copyright Office to allow an exemption to the general prohibition on circumvention of copyright protection systems under the Digital Millennium Copyright Act of 1998 for unlocking of phones through user self-help (sometimes referred to as "hacking"). This exemption has become less important now that most carriers are voluntarily providing unlock codes.
According to a ruling effective October 28, 2012, it will be illegal to unlock phones purchased 90 days after this date or later without the carrier's permission. In other words, users can already unlock phones they already own, and phones purchased before January 29, 2013, but phones purchased after this point can only be unlocked with the carrier's permission.
On August 1, 2014, President Obama signed into law the Unlocking Consumer Choice and Wireless Competition Act (S. 517; 113th Congress), a bill legalizing unlocking cellphones in the U.S. The bill passed in the United States Senate on July 15, 2014, and in the United States House of Representatives on July 25, 2014.
It is possible to buy unlocked phones in the US. Online retailers such as GSM Nation sell phones that come unlocked from the manufacturer, that is, they were never locked in the first place.
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