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A telephone number or phone number is a sequence of digits used to call from one telephone line to another in a public switched telephone network. When telephone numbers were invented, they were short — as few as one, two or three digits — and were given orally to a switchboard operator. As phone systems have grown and interconnected to encompass the world, telephone numbers have become longer. In addition to telephones, they now access other devices, such as computers and fax machines.
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, 0-0-0, 9-9-9, 1-1-1, and 1-1-2 being the Emergency Services numbers for China, Japan, 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.)
Many systems also allow calls within a local area to be made without dialing the local area code. For example, a phone number in North America will start with three numbers (such as 661), which is the area code, followed by seven digits split into sections of three and four (such as 550-1212), which is the local number. Some areas now have mandatory ten-digit dialing in place, even for local calls.
Most telephone networks today (exceptions being private intercom and secure phone networks) are interconnected in the international telephone network, where the format of telephone numbers is standardized by ITU-T in the 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 fixed line phone, the + must be replaced with the international call prefix chosen by the country the call is being made from. Some mobile phones allow the + to be entered directly.
US phone number history 
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.
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 a 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 the event of 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 North America, the digits 2–9 of phone numbers were allotted 3 letters of the alphabet apiece. This left room for only 24 letters, so the uncommon letters Q and Z were omitted.
Phone numbers were not so usually strictly numeric until the mid-1960s. From the 1920s until then, most urban areas had "exchanges" of two letters, followed by numbers, e.g., EDgewood, IVanhoe. In the UK, exchanges in the major cities with Director installations were represented by three letters followed by four numbers; the letters usually represented the name of the exchange area, e.g., MAYfair, WATerloo, or something memorable about the locality (e.g., POPesgrove — an area where Alexander Pope once lived). This was considered easier to remember, although in London in the later part of this period it required the memorization of 7 characters (roughly the same number of characters as is usual for local calling in 2008). A word would represent the first two digits to be dialed, for example "TWinbrook" for "89" ; "BYwater" for "29". UK numbers had no letters at all except for those in the Director areas, where the first three of the seven digits were assigned letters, and written "ABBey 1234" or "WHItehall 1212", for example. A lack of pronounceable words, and the fact that most telephones world-wide have no letters on anyway, have led to the abandonment of letter usage in directory numbers except for publicity purposes.
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 3 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 from running out of available numbers.
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 
The "555" (or Klondike-5) exchange was never assigned any real numbers (with limited exceptions such as 555-1212 for directory assistance), which is why today's TV and movie shows use 555-xxxx numbers for their phone numbers (previously, such productions often used numbers that ended in certain four-number combinations that were typically set aside for similar uses — "0079" on the West Coast and "9970" in many other places; examples include the TV series Perry Mason and the 1948 film Sorry, Wrong Number). "Klondike-5" was also heard in the Perry Mason show and in Seinfeld.
That way there was no possibility that a fake number from a show would actually reach someone, thus avoiding the scenario which arose in 1982 with Tommy Tutone's hit song "867-5309/Jenny". This song led to many customers who actually had that number receiving a plethora of unwanted calls. In fact, many American phone companies either no longer assign this number, or they have relegated it to internal testing purposes. As of early August 2009, (267) 867-5309, which is assigned to the suburban Philadelphia area, was being auctioned on eBay. Bidding is in excess of $5,000 USD.
However, today only numbers beginning with 555-01xx are reserved for fiction and other 555-numbers can be allocated to "information providers". A side effect of the fictional-number pool being reduced to 100 numbers is that the same ones now often recur in different movies or TV shows. The "958" and "959" exchanges have also been reserved for similar purposes in most localities, and as a result very few individuals or businesses have telephone numbers beginning with those sets of digits either (although this fact is not as well known, so such numbers have not been used in a fictional context).
The number in the Glenn Miller Orchestra's hit song "Pennsylvania 6-5000" is the number of the Hotel Pennsylvania in New York City, and was issued in 1919. The number is now written as (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.
In 2003, the movie Bruce Almighty originally featured a number that did not have the 555 prefix. In the movie, God (Morgan Freeman) left the number for Bruce Nolan (Jim Carrey) to call if he needed God's help. 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 was reportedly changed when the movie was released on DVD. Martin Scorsese's After Hours contains a working phone number in it, 243-3460, but no area code is explicitly given.
In the Disney film The Computer Wore Tennis Shoes, a 247 number was given to a pay phone. This was because the writer of the script, Joe McEveety, used his own number in the film. In a scene from another Disney film, Bolt, the number (877) 504-8423 is seen printed on a flyer. The number is reserved by ABC, as evidenced by the brief recorded message heard when the number is called, which reads "Thank you for calling ABC. The number you have reached is a fictional non-working number used for motion picture and television production."
The 1995 film Heat contains phone numbers for pay phones that have 1 as the first digit. One such number, for a pay phone read by Danny Trejo's character to Robert De Niro's, is 103-7206.
United Kingdom 
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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.
Intercepted number 
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, it went to an intercept operator who informed the caller. In the 1970s this service was converted to Automatic Intercept Systems which automatically chooses and presents 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.
See also 
- Category:Telephone numbers by country
- Geographic number
- List of country calling codes
- Local conventions for writing telephone numbers
- Long distance calling
- Area code
- Number translation service
- Telephone numbering plan
- Voice over IP
- 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)
- International Correspondence Schools (1916). "Subscribers' Station Equipment". International Library of Technology (Internal Textbook Company). p. 20. Retrieved 2008-05-27.
- [dead link]
- New York's Hotel Pennsylvania
- "Almighty" Phone Mess. CBS News, 27 May 2003. Retrieved on 2009-05-04.
- 'Bruce Almighty' delivers wrong number. People Online. Retrieved on 2009-05-04.
- 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.