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North American Numbering Plan

The North American Numbering Plan is the system for three-digit area codes that direct telephone calls to particular regions on a public switched network (PSTN), where they are further routed by the local network. It is now applied to the United States and its territories, Canada, Bermuda, and many Caribbean nations.

NANP was instituted by AT&T, then the U.S. telephone monopoly, in 1947.

Originally there were 86 codes, with the biggest population areas getting the numbers that took the shortest time to dial on rotary phones. That's why New York City was given 212 (a total of 5 clicks) and Los Angeles given 213, while Vermont received 802 (a total of 20 clicks).

At first, area codes were in the form N-Y-X, where N is any number 2-9, Y is 0 or 1, and X is any number 1-9.

The restriction on N saves 0 for calling the operator, and 1 for signaling a long-distance call.

The restriction on the second digit, limiting it to 0 or 1, was designed to help telephone equipment recognize the difference between a three-digit area code and a three-digit prefix to the telephone number. For example, when a caller dialed 202-555-1212, the switching equipment would recognize that 202 was an area code because of the middle 0, and route the call appropriately.

As of 1995, an increase in the need for more area codes made officials drop this restriction. This has produced some confusion, because area codes can now be the same as telephone prefixes. Nashua, New Hampshire, for example, has a local exchange that begins 888, which is also an area code for toll-free calls. If somebody in Nashua means to call 1-888-555-1212 but forgets the initial "1" they will actually dial the local number 888-5551.

In TV shows and movies originating in the USA, 555 is used as the first three digits of fictional telephone numbers so that if anyone is tempted to telephone a number seen on screen, it does not cause a nuisance to any actual person. However, not all numbers that begin with "555[?]" are fictional--for example, 555-1212[?] is the number for directory assistance[?] in many places. In fact, only 555-0100 through 555-0199 have been specifically reserved for fictional use.

The North American Numbering Plan is now overseen by the private company NeuStar Inc.[?]

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