A telephone number is a sequence of digits assigned to a fixed-line telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices for data transmission via the public switched telephone network (PSTN) or other private networks. Most telephone numbers are assigned to one telephone line or one mobile telephone, and most lines or mobiles have one number.
A telephone number serves as an address for switching telephone calls using a system of destination routing. Telephone numbers are entered or dialed by a calling party on the originating telephone set, which transmits the sequence of digits in the process of signaling to a telephone exchange. The exchange completes the call either to another locally connected subscriber or via the PSTN to the called party.
The use of telephone numbers instead of subscriber names to indicate to the telephone operator what destination line a caller wished to be connected to was developed and first used in the autumn of 1879 in Lowell, Massachusetts during a measles epidemic. Moses Greeley Parker, a local doctor, realized that if all four of the city's operators were incapacitated by the epidemic, their replacements would have great trouble quickly learning which of the switchboard's 200 jacks were assigned to which subscribers. He recommended the use of numbers instead. "The local Bell company management at first protested that its customers would consider their designation by numbers to be beneath their dignity; nevertheless, it saw the logic of the doctor's suggestion and followed it. The subscribers were not outraged; the epidemic quickly passed, but telephone numbers did not."
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When telephone numbers were first used they were very short, from one to three digits, and were communicated orally to a switchboard operator when initiating a call. As telephone systems have grown and interconnected to encompass worldwide communication, telephone numbers have become longer. In addition to telephones, they have been used to access other devices, such as computer modems, pagers, and fax machines. With landlines, modems and pagers falling out of use in favor of all-digital always-connected broadband Internet and mobile phones, telephone numbers are now instead taken by data-only cellular devices, such as some tablet computers, digital cameras, and even game controllers and mobile hotspots, on which it is not even possible to make or accept a phone call.
The number contains the information necessary to identify uniquely the intended endpoint for the telephone call. Each such endpoint must have a unique number within the public switched telephone network. Most countries use fixed length numbers (for normal lines at least) and therefore the number of endpoints determines the necessary length of the telephone number. It is also possible for each subscriber to have a set of shorter numbers for the endpoints most often used. These "shorthand" or "speed calling" numbers are automatically translated to unique telephone numbers before the call can be connected. Some special services have their own short numbers (e.g., 1-1-9, 9-1-1,1-0-0, 0-0-0, 9-9-9, 1-1-1, and 1-1-2 being the Emergency Services numbers for China, Japan, India, South Korea, Taiwan and Sri Lanka; Canada and the United States; Australia; the United Kingdom, Ireland, South Africa, Poland, Saudi Arabia, the United Arab Emirates, Morocco, Macao, Bahrain, Qatar, Bangladesh, Botswana, Ghana, Kenya, Hong Kong, Malaysia, Mauritius, Singapore, Zimbabwe, Trinidad, Tobago; New Zealand; Kuwait and the European Union, respectively.)
The dialing plan in some areas permits dialing numbers in the local calling area without using area code or city code prefixes. For example, a telephone number in North America consists of a three-digit area code, a three-digit central office code, and four digits for the line number. If the area has no area code overlays, seven-digit dialing may be permissible for calls within the area, but some areas have implemented mandatory ten-digit dialing.
Other special phone numbers are used for high-capacity numbers with several telephone circuits, typically a request line to a radio station where dozens or even hundreds of callers may be trying to call in at once, such as for a contest. For each large metro area, all of these lines will share the same prefix (such as 404-741-xxxx in Atlanta and 305-550-xxxx in Miami), the last digits typically corresponding to the station's frequency, callsign, or moniker.
In the international telephone network, the format of telephone numbers is standardized by ITU-T recommendation E.164. This specifies that the entire number should be 15 digits or shorter, and begin with a country prefix. For most countries, this is followed by an area code or city code and the subscriber number, which might consist of the code for a particular telephone exchange. ITU-T recommendation E.123 describes how to represent an international telephone number in writing or print, starting with a plus sign ("+") and the country code. When calling an international number from a landline phone, the + must be replaced with the international call prefix chosen by the country the call is being made from. Many mobile phones allow the + to be entered directly, by pressing and holding the "0" for GSM phones, or sometimes "*" for CDMA phones.
The format and allocation of local phone numbers are controlled by each nation's respective government, either directly or by sponsored organizations (such as NANPA in the US or CNAC in Canada). In the United States, each state's public service commission regulates, as does the Federal Communications Commission. In Canada, which shares the same country code with the U.S. (due to Bell Canada's previous ownership by the U.S.-based Bell System), regulation is mainly through the Canadian Radio-television and Telecommunications Commission.
Teleconversion is the process or act of changing one's telephone number while remaining with the same telephone company, often due to relocation. Conversely, local number portability (LNP) allows a person to move his or her existing phone number to another carrier. The two processes converge in the instance of a port-in teleconversion, where an existing number is changed to one which is brought from another carrier. This may occur where a person takes a wireline number (such as a home business) and ports it to an existing cellphone (possibly a wireless home phone), or where a new line is activated but the port-in request is still pending, the teleconversion then occurring when the porting process successfully completes.
Number portability usually has geographic limitations, such as an existing local phone company only being able to port to a competitor within the same rate centre. Mobile carriers may have much larger regions called markets, which can assign or accept numbers from any area within the region; these markets vary depending on carrier.
Within most North American rate centres, local wireline calls are free, while calls to all but a few nearby rate centres are considered long distance and incur a per-minute toll. In a few large US cities, as well as most points outside North America, local calls are not flat-rated or "free" by default.
The world's largest toll-free calling areas are the Atlanta metropolitan area (CSA pop 6,162,195) and Greater Toronto Area (CMA pop 5,583,064) exchanges reachable locally from the respective downtown rate centres. Both span multiple area codes in some combination of split plans and overlay plans.
In the late 1870s, the Bell interests started utilizing their patent with a rental scheme, in which they would rent their instruments to individual users who would contract with other suppliers to connect them; for example from home to office to factory. Western Union and the Bell company both soon realized that a subscription service would be more profitable, with the invention of the telephone switchboard or central office. Such an office was staffed by an operator who connected the calls by personal names. Some have argued that use of the telephone altered the physical layout of American cities. 
The latter part of 1879 and the early part of 1880 saw the first use of telephone numbers at Lowell, Massachusetts. During an epidemic of measles, the physician, Dr. Moses Greeley Parker, feared that Lowell's four telephone operators might all succumb to sickness and bring about paralysis of telephone service. He recommended the use of numbers for calling Lowell's more than 200 subscribers so that substitute operators might be more easily trained in such an emergency. Parker was convinced of the telephone's potential, began buying stock, and by 1883 he was one of the largest individual stockholders in both the American Telephone Company and the New England Telephone and Telegraph Company.
Even after the assignment of numbers, operators still connected most calls into the early 20th century: "Hello, Central. Get me Underwood-342." Connecting through operators or "Central" was the norm until mechanical direct-dialing of numbers became more common in the 1920s.
In rural areas with magneto crank telephones connected to party lines, the local phone number consisted of the line number plus the ringing pattern of the subscriber. To dial a number such as "3R122" meant making a request to the operator the third party line (if making a call off your own local one), followed by turning the telephone's crank once, a short pause, then twice and twice again. Also common was a code of long and short rings, so one party's call might be signaled by two longs and another's by two longs followed by a short. It was not uncommon to have over a dozen ring cadences (and subscribers) on one line.
In the most areas of North America, telephone numbers in metropolitan communities consisted of a combination of digits and letters, starting in the 1920s until the 1960s. Letters were translated to dialed digits, a mapping that was displayed directly on the telephone dial. Each of the digits 2 to 9, and sometimes 0, corresponded to a group of typically three letters. The leading two or three letters of a telephone number indicated the exchange name, for example, EDgewood and IVanhoe, and were followed by 5 or 4 digits. The limitations that these system presented in terms of usable names that were easy to distinguish and spell, and the need for a comprehensive numbering plan that enabled direct-distance dialing, led to the introduction of all-number dialing in the 1960s.
The use of numbers starting in 555- (KLondike-5) to represent fictional numbers in U.S. movies, television, and literature originated in this period. The "555" prefix was reserved for telephone company use and was only consistently used for directory assistance (information), being "555-1212" for the local area. An attempt to dial a 555 number from a movie in the real world will always result in an error message when dialed from a phone in the United States. This reduces the likelihood of nuisance calls. Also, QUincy(5-5555) was used, because there was no Q available. Phone numbers were traditionally tied down to a single location; because exchanges were "hard-wired", the first three digits of any number were tied to the geographic location of the exchange.
Alphanumeric telephone numbers
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Because the switches were hard-wired together and fairly hard to re-wire (or re-grade), telephone exchange buildings in many larger cities in North America were dedicated to circuits that began with the first two or three digits of the standard 7 digit phone numbers. In a holdover from the days of plug-board exchanges, the exchanges were typically named with a name whose first two letters translated to the digits of the exchange's prefix on a common telephone dial. Examples: CAstle (22), TRinity (87), MUtual (68), and KLondike (55). Certain number combinations were not amenable to this naming process, such as "57," "95" and "97". It was in part due to this factor that telephone exchange names were finally abandoned, since more numbers were needed to prevent a given area code.
In the past, the first two or three digits could be represented by a mnemonic exchange name, e.g., 869-1234 was formerly TOwnsend 9-1234, and before that (in some localities) might have been TOWnsend 1234 (only the capital letters and numbers being dialed) or it could have been TOwnsend 1234 (86-1234)
In December 1930, New York City became the first city in the United States to adopt the two-letter, five-number format. It remained alone in this respect until well after World War II, when other municipalities across the country began to follow suit. From the 1920s through the 1950s, most larger American cities used the Bell System standard format of two letters which began the exchange name followed by four numbers, as in DUnkirk 0799. Prior to the mid-1950s, the number immediately following the name could never be a "0" or "1" - indeed, "0" was never pressed into service at all, except in the immediate Los Angeles area. (The "Bensonhurst 0" exchange mentioned in an episode of the former TV sitcom The Honeymooners was a fictitious one.)
In 1955, the Bell System attempted to standardize the process of naming exchanges by issuing a "recommended list" of names to be used for the various number combinations. In 1961, the New York Telephone Company introduced "selected-letter" exchanges, in which the two letters did not mark the start of any particular name (example: LT 1-7777, once the number of the main switchboard at ABC ), and by 1965 all newly connected phone numbers nationwide consisted of numerals only. (Wichita Falls, Texas, had been the first locality in the United States to implement the latter, having done so in 1958.) Pre-existing numbers continued to be displayed the old way in many places well into the 1970s. For example, Boushelle, a company outside Chicago, still uses HUdson3-2700 in their commercials.
Because the pulses from a rotary dial (as used to operate switches in a Strowger exchange) took time, having a phone number with lots of 8s, 9s, or 0s meant it took longer to dial the number. The phone companies typically assigned such "high" numbers to pay phones because they were rarely dialed to.
In popular culture
Australian films and television shows do not employ any recurring format for fictional telephone numbers; any number quoted in such media may be used by a real subscriber. The 555 code is used in the Balmain area of Sydney and the suburbs of Melbourne. Although in many areas being a prefix of 55 plus the thousand digit of 5 (e.g. 55 5XXX), would be valid, the numbering system was changed so that 555 became 9555 in Sydney and Melbourne, and in the country, there are 2 new digits ahead of the 55.
However, elsewhere, as in the United States, fictitious telephone numbers are often used in films and on television to avoid disturbances by calls from viewers. For example, The United States 555 (KLondike-5) exchange code was never assigned (with limited exceptions such as 555-1212 for directory assistance). Therefore, American films and TV shows have used 555-xxxx numbers, in order to prevent a number used in such a work from being called.
The film Bruce Almighty (2003) originally featured a number that did not have the 555 prefix. In the cinematic release, God (Morgan Freeman) leaves 776-2323 on a pager for Bruce Nolan (Jim Carrey) to call if he needed God's help. The DVD changes this to a 555 number. According to Universal Studios, which produced the movie, the number it used was picked because it did not exist in Buffalo, New York, where the movie was set. However, the number did exist in other cities, resulting in customers' having that number receiving random calls from people asking for God. While some played along with the gag, others found the calls aggravating.
The number in the Glenn Miller Orchestra's hit song "Pennsylvania 6-5000" (1940) is the number of the Hotel Pennsylvania in New York City. The number is now written as 1-212-736-5000. According to the hotel's website, PEnnsylvania 6-5000 is New York's oldest continually assigned telephone number and possibly the oldest continuously-assigned number in the world.
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In the UK, letters were assigned to numbers in a similar fashion as in North America, except that the letter O was allocated to the digit 0 (zero); digit 6 had only M and N. The letter Q was later added to the zero position on British dials, in anticipation of direct international dialing to Paris which commenced in 1963. This was necessary because French dials already had Q on the zero position, and there were exchange names in the Paris region which contained the letter Q.
Most of the United Kingdom had no lettered telephone dials until the introduction of Subscriber Trunk Dialing (STD) in 1958. Prior to that time, only the director areas (Birmingham, Edinburgh, Glasgow, Liverpool, London and Manchester) and the adjacent non-director areas had the lettered dials; the director exchanges used the three-letter, four-number format. With the introduction of trunk dialing, the need for all callers to be able to dial numbers with letters in them led to the much more widespread use of lettered dials. The need for dials with letters was finally abandoned with the conversion to all-digit numbering in 1968.
In the middle 20th century in North America when a call could not be completed, for example because the phone number was not assigned, had been disconnected, or was experiencing technical difficulties, the call was routed to an intercept operator who informed the caller. In the 1970s this service was converted to Automatic Intercept Systems which automatically choose and present an appropriate intercept message. Disconnected numbers are reassigned to new users after the rate of calls to them declines.
Outside of North America operator intercept was rare, and in most cases calls to unassigned or disconnected numbers would result in a recorded message or number-unobtainable tone being returned to the caller.
- Category:Telephone numbers by country
- Geographic number
- List of country calling codes
- National conventions for writing telephone numbers
- Long distance calling
- Number translation service
- Phonewords and vanity numbers
- Telephone numbering plan
- Zenith number
- Caller ID
- Automatic number identification (ANI)
- Automatic number announcement circuit (ANAC)
- Dialed Number Identification Service (DNIS)
- Loop around
- Carrier access code (CAC)/Carrier identification code (CIC)
- Brooks, John. Telephone: The First Hundred Years. Harper & Row, 1967, ISBN 0-06-010540-2: p. 74, citing "Events in Telephone History".
- Fischer, Claude S. America Calling: A Social History of the Telephone to 1940. Berkeley: University of California Press, 1992. Web.
- International Correspondence Schools (1916). Subscribers' Station Equipment. International Library of Technology (Internal Textbook Company). p. 20. Retrieved 2008-05-27.
- Cuccia, Mark. "CODE 555 AND THE MOVIES". Telecom Heritage (27) (Australian Telephone Collectors Society Inc.).
- Vries, Lloyd (27 May 2003). "'Almighty' Phone Mess". CBS News.
- 'Bruce Almighty' delivers wrong number. People Online. Retrieved on 2009-05-04.
- Carlson Jen (2 July 2014). "The Oldest Phone Number In NYC". Gothamist.
- "Old New York: Historical Attractions". Hotel Pennsylvania. 23 January 2014. New York.
- Mikkelson, Barbara (9 July 2014). "867-5309 / Jenny". Snopes.com.
- ITU-T Recommendation E.123: Notation for national and international telephone numbers, e-mail addresses and Web addresses
- RFC 3966 The
tel:URI for telephone numbers
- History of UK dialing codes, with lists of codes and more links
- World Telephone Numbering Guide which can be used to look up telephone numbering information
- ITU National Numbering Plans which links to the numbering plans of individual countries.
- Cybertelecom :: VoIP :: Numbers Detailing FCC policy regarding legacy NANP telephone numbers and interconnected VoIP services
- ATIS, Industry Numbering Committee