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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.
This was followed quickly by area code 520 serving Arizona on March 19, 1995. By 1995, many cities in the United States and Canada had more than one area code, either from dividing a city into different areas (NPA split) or having more than one code for the same area (NPA overlay).
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.
Requirements [ edit ] U.S. Carriers holding any Central Office Codes are required to submit information regarding their own numbering resource usage to the NANPA twice yearly, by February 1 and August 1 of each year, as required under CFR Title 47, Volume 3, Section 52 (f)(6)(i). [ 1 ]
Area code 602 is the oldest area code in Arizona and was assigned in 1947 for the entire state. Under pressure from population growth and new telecommunications services, the numbering plan area (NPA) was reduced twice in five years in the 1990s. In 1995, the state outside metropolitan Phoenix was split off with area code 520.
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
For this size of the network, a unique two-digit code for each numbering plan area (NPA) would have been sufficient. However, AT&T wanted to preserve existing dialing practices by only dialing the local number for local calls; it was therefore necessary to distinguish the NPA codes from central office codes automatically by the switching system.
Valley National Bank of Arizona; W. Western Alliance Bancorporation This page was last edited on 23 December 2023, at 23:26 (UTC). ...