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NANP telephone numbers are usually rendered as NPA-NXX-XXXX or (NPA) NXX-XXXX. For example, 250 555 0199, a fictional number, could be rendered as 250-555-0199, (250) 555-0199, 250-5550199, or 250/555-0199. The parentheses were originally used to indicate that the area code was not necessary for local dialing.
Public resistance to the introduction of new area codes, whether as overlay complexes (which allowed customers to keep their existing numbers, but broke seven-digit local calling) or by area code splits (where the area code of existing numbers was changed), prompted the FCC and state commissions to introduce thousands-block number pooling, i.e. the allocation of number space in blocks of only ...
Each rate center is associated with: a geographical place name (city, province/state) a nominal physical location (V and H co-ordinates) for distance calculations for billing purposes; one or more prefixes, in the form +1-NPA-NXX, which each identify a block of ten thousand directory numbers
Thus, NXX is a number from 200 through 999, while XXXX is a range from 0000 through 9999. The first three digits of a telephone number are the numbering plan area code (NPA code, or simply NPA). The next three, NXX, identify the central office and the last four digits are the line number of an individual office.
From 1947 to 1995, all NPA codes were distinguished with the digits 0 or 1 in the middle position. This provided the traditional format N 0/1 X, where N is any digit from 2 to 9, and X is any of the ten numerals. This format provided a set of 160 combinations, but only 144 were in use for geographic NPA codes.
In the administration of the North American Numbering Plan, central office code protection is a numbering policy for maintaining local seven-digit dialing in communities that extend on both sides of the boundary line between multiple numbering plan areas (NPAs), such as in cross-border towns on state lines.
NPA-911 is forbidden as 9-1-1 is an emergency telephone number. (This is less restrictive than the rules prohibiting all three-digit N-1-1 codes as exchanges in all geographic area codes.) NPA-555 is reserved in every toll-free area code (except 800) for future information or directory assistance applications
The traditional convention for phone numbers is (0AA) NXX-XXXX, where 0AA is the area code and NXX-XXXX is the subscriber number. This number format is very similar to the North American numbering plan, but the country has a trunk code of 0 instead of 1, so international callers (using +81) do not have to dial the trunk code 0 when calling to ...