An SMS gateway allows a computer to send or receive Short Message Service (SMS) transmissions to or from a telecommunications network. Most messages are eventually routed into the mobile phone networks. Many SMS gateways support media conversion from email and other formats.
Several mobile telephone network operators have true fixed-wire SMS services. These are based on extensions to the European Telecommunications Standards Institute (ETSI) Global System for Mobile Communications (GSM) SMS standards and allow messaging between any mix of fixed and mobile equipment. These use frequency-shift keying to transfer the message between the terminal and the SMSC. Terminals are usually based on Digital Enhanced Cordless Telecommunications (DECT), but wired handsets and wired text-only (no voice) devices exist. Messages are received by the terminal recognising that the Caller ID is that of the SMSC and going off-hook silently to receive the message.
GSM gateway appliance
A direct-to-mobile gateway is a device which has built-in wireless GSM connectivity. It allows SMS text messages to be sent and/or received by email, from Web pages or from other software applications by acquiring a unique identifier from the mobile phone's Subscriber Identity Module, or "SIM card". Direct-to-mobile gateways are different from SMS aggregators, because they are installed on an organization's own network and connect to a local mobile network.
The connection to the mobile network is made by acquiring a SIM card number from the mobile operator and installing it in the gateway. Typically, direct-to-mobile gateway appliances are used for hundreds to thousands of text messages per month. More modern appliances now offer the capability of send up to 100,000 messages each day. Several vendors that have historically provided GSM Gateway equipment for voice also have SMS capability. Some are more primitive than others. The more capable devices are designed with SIM management to regulate the number of SMS messages per SIM, ODBC to connect to a database, and HTTP interfaces to interact with third party applications.
GSM gateway equipment is covered by the Wireless Telegraphy Act in the UK and can legally be used by any business to send SMS to their own customers or prospects when using their own gateway equipment. In Canada, SMS gateway providers are regulated by the Canadian Wireless Telecommunications Association (CWTA/txt.ca). In India it is regulated by the Telecom Regulatory Authority of India (TRAI). In Pakistan it is regulated by the Pakistan Telecommunication Authority(PTA).
A direct-to-short message service center (SMSC) gateway is a software application, or a component within a software application, that connects directly to a mobile operator's SMSC via the Internet or direct leased line connections. The Short Message Peer-to-Peer (SMPP) protocol is typically used to convey SMS between an application and the SMSC. Direct-to-SMSC gateways are used by SMS aggregators to provide SMS services to their clients and large businesses who can justify such use. They are typically employed for high volume messaging and require a contract directly with a mobile operator.
An SMS gateway typically sits between the end user who needs to send/receive SMS and a mobile network's SMSC. Such gateways provide a choice of protocols, including HTTP, SMTP, SMPP and Web services. Providers of SMS gateway services include SMS aggregators and mobile operators. SMS gateways are also available as part of messaging services such as AOL, ICQ and others.
An SMS gateway connects with (i) mobile network SMSCs in order to send/receive messages and/or (ii) other SMS gateways in order to reach mobile subscribers on multiple mobile networks. It is therefore possible that an SMS gateway has a combination of mobile network SMSC connections and connections with other SMS gateways in order to provide its services. However, there is the increasing potential for delivery problems with SMS the greater the number of SMS gateways in the delivery chain.
AOL Instant Messenger
Microsoft Outlook 2007 has native support for sending SMS messages worldwide via the Outlook Mobile Service. There are also plug-ins for Microsoft Outlook that add this functionality. This uses the SMS gateways of aggregators or of mobile operators.
Skype has support for sending SMS messages. SMS sent through Skype can be configured to appear as originating from the Skype user's cellphone.
Windows Live Messenger
MSN Messenger (Windows Live Messenger) 7.0 and up have support for SMS messages.
Use with email clients
Text messages can be sent from a personal computer to mobile devices via an SMS gateway, using most popular email client programs, such as Outlook, Thunderbird, and so on. The messages must be sent in ASCII "text-only" mode. If they are sent in HTML mode, or using non-ASCII characters, they will most likely appear as nonsense on the recipient's mobile telephone.
Before the message can be sent, one must determine the domain of the mobile carrier's SMS gateway. For example, if one wanted to send a message to a mobile telephone in the United States serviced by AT&T, and the telephone number is +1 415-123-4567, the email would be addressed as
To determine the SMS gateway domain, e.g.,
txt.att.net, may require research, as mobile telephone users typically do not know this information when they provide their telephone number and due to number portability the number may no longer be associated with the carrier that originally issued it. Observe that the telephone number in this example is expressed as ten (10) digits, without the country code (1) and without dashes or other separator characters when composing the email address. The country code is not needed, as the 10-digit telephone number, together with the email domain, are sufficient to send the email from any location in the world.
It is useful to perform a character count before sending the message to ensure that it is within the 160-character limit. If it exceeds the limit, the SMS gateway should break the message into a set of consecutive 160-character, or shorter, messages to the mobile equipment, although the breaks may occur in the middle of words.
A message sent with an email client can be simultaneously addressed to multiple mobile telephones, whereas text messages sent in the usual manner between mobile telephones can only be sent to a single recipient.