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Telephone numbers listed in 1920 in New York City having three-letter exchange prefixes. In the United States, the most-populous cities, such as New York City, Philadelphia, Boston, and Chicago, initially implemented dial service with telephone numbers consisting of three letters and four digits (3L-4N) according to a system developed by W. G. Blauvelt of AT&T in 1917. [1]
Toll-free telephone numbers in the North American Numbering Plan have the area code prefix 800, 833, 844, 855, 866, 877, and 888. Additionally, area codes 822, 880 through 887, and 889 are reserved for toll-free use in the future. 811 is excluded because it is a special dialing code in the group NXX for various other purposes.
The North American Numbering Plan (NANP) divides the territories of its members into geographic numbering plan areas (NPAs). Each NPA is identified by one or more numbering plan area codes (NPA codes, or area codes), consisting of three digits that are prefixed to each local telephone number having seven digits.
All-number calling was a telephone numbering plan introduced in 1958, [35] that converted telephone numbers with exchange names to a numeric representation of seven digits. The original plan of 1947 had been projected to be usable beyond the year 2000. However, by the late 1950s it became apparent that it would be outgrown by about 1975. [36]
A telephone prefix is the first set of digits after the country, and area codes of a telephone number. In the North American Numbering Plan countries (country code 1), it is the first three digits of a seven-digit local phone number, the second three digits of the 3-3-4 scheme. In other countries, both the prefix and the number may have ...
The Local Exchange Routing Guide (LERG) is a database of telecommunications numbering resources for use in the administration and operation of the North American Numbering Plan (NANP) by the NANP administrator (NANPA) and telecommunications service providers. This data supports the local exchange network of the NANP and identifies planning ...