North American Numbering Plan - History

History

In order to facilitate direct dialing calls, the NANP was created and instituted in 1947 by AT&T, also known as the Bell System, the U.S. telephone semi-monopoly. At first, the codes were used only by long-distance operators; the first customer-dialed calls using area codes did not occur until November 10, 1951, when the first directly dialed call was made from Englewood, New Jersey to Alameda, California. Direct dialing was gradually instituted throughout the country, and by the mid-1960s, it was commonplace in most larger cities.

Originally there were only 86 codes, with the biggest population areas getting the numbers that took the shortest time to dial on rotary telephones. Thus, five largest cities based on 1950 US Census population received some of the "shortest" codes: New York City was given 212, Chicago 312, Los Angeles 213, Detroit 313, Philadelphia 215; while four areas received the then-maximum number of 21 clicks: South Dakota (605), North Carolina (704), South Carolina (803), and the Maritime Provinces of Canada (902). Additionally, in the original plan a middle digit of 0 indicated that the area code covered an entire state/province, while area codes with a middle digit of 1 were assigned to jurisdictions that were divided into multiple area codes.

At first, area codes were all in the form NYX, where N is any number 2–9, Y is 0 or 1, and X is any number 1–9 (if Y is 0) or any number 2–9 (if Y is 1). 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" (with 0 or 1 as the second digit) and the three-digit "exchange" prefix (which had avoided 0 or 1 for the second digit, because of restrictions in existing switching equipment). 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. If a caller were to dial 345-6789, the 4 would cause the number to be recognized as a long-distance number within the area and routed as such, without waiting for the caller to finish dialing.

In the late 1980s and early 1990s, NANPA (then still part of Bellcore, which is now Telcordia Technologies) began to urge and later require all long-distance calls within each area to be prefixed with the digit 1 to distinguish them from local calls, so that badly needed prefixes with 0 or 1 in the middle could be assigned to local telephone exchanges. Also, since it had nearly run out of area codes using the above formula, it allowed the assignment of area codes using the form N10, such as 210 in the San Antonio, Texas, area and 410 in eastern Maryland. Therefore, someone calling from San Jose to Los Angeles before the change would have dialed 213-555-1234 and after the change 1-213-555-1234, which then allowed 213 to be used as an exchange prefix in the San Jose area.

Until 1991, calls to some areas of Mexico from the United States and Canada were made using NANP area codes, but Mexican participation in the NANP was discontinued in favor of the general international format, using country code +52 instead. Area Code 905 (formerly Mexico City) was re-assigned to the Greater Toronto Area outside of Toronto (which retained Area Code 416), and Area Code 706 (formerly northwest Mexico) was reassigned to northern Georgia, surrounding the Atlanta region which retained 404.