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An area code overlay is a numbering plan area (NPA) in the North American Numbering Plan (NANP) that has multiple area codes assigned. Overlay complexes are used to add central office prefixes in an NPA to increase the number of available telephone numbers. [1]
The North American Numbering Plan (NANP) is a telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1 and has the telephone country code 1. Some North American countries, most notably Mexico, do not participate with the NANP.
Area codes 314 and 557 are telephone area codes in the North American Numbering Plan (NANP) in the U.S. state of Missouri, serving the city of St. Louis and most of its inner-ring suburbs in neighboring St. Louis County. The numbering plan area is bordered to the west by area code 636, which serves St. Louis' outer suburbs to the west, south, and north. Across the Mississippi River to the east, 314 is adjacent to area code 618, which serves southern Illinois and most of Metro East. Area code 557 was added to the 314 numbering plan area on August 12, 2022, to form an overlay numbering plan.
Area codes 415 and 628 are telephone area codes in the North American Numbering Plan (NANP) for the city of San Francisco and its northern suburbs in Marin County, and the northeast corner of San Mateo County in the U.S. state of California. Area code 415 was one of the eighty-six original North American area codes established in 1947, but modified in geographic configuration later. Area code 628 was assigned in 2015 to form an overlay in that numbering plan area in mitigation of central office prefix exhaustion.
Area codes 920 and 274 are telephone area codes in the North American Numbering Plan (NANP) for a large area of eastern Wisconsin. Area code 920 was created on July 26, 1997, in a split of area code 414, one of the original North American area codes of 1947. 274 was added to the same numbering plan area (NPA) on May 5, 2023 to create an area code overlay.
Area code 564 is a telephone overlay area code in the North American Numbering Plan (NANP) for Western Washington state, including metropolitan Seattle. The area code was first proposed in 1999 to relieve telephone number shortages in area code 360, but implementation was delayed until 2017, when it was installed for an overlay complex that comprises only the numbering plan area 360. Neighboring area codes 206, 253, and 425 were slated for expansion of the overlay upon exhaustion of central office codes in each NPA. In 2023, area code 206 was approved for expansion with a guide line for preparation of inclusion of at least nine months. Ten-digit dialing has been mandatory in all of western Washington since July 29, 2017.
Telephone number pooling, thousands-block number pooling, or just number pooling, is a method of allocating telephony numbering space of the North American Numbering Plan in the United States. The method allocates telephone numbers in blocks of 1,000 consecutive numbers of a given central office code to telephony service providers. In the United States it replaced the practice of allocating all 10,000 numbers of a central office prefix at a time. Under number pooling, the entire prefix is assigned to a rate center, to be shared among all providers delivering services in that rate center. Number pooling reduced the quantity of unused telephone numbers in markets which have been fragmented between multiple service providers, avoided central office prefix exhaustion in high growth areas, and extended the lifetime of the North American telephone numbering plan without structure changes of telephone numbers. Telephone number pooling was first tested for area code 847 in Illinois in June 1998, and became national policy in a series of Federal Communications Commission (FCC) orders from 2000 to 2003.
Area code 917 is a telephone area code in the North American Numbering Plan for the five boroughs of New York City: The Bronx, Brooklyn, Manhattan, Queens, and Staten Island. It is an overlay code to all numbering plan areas (NPAs) in the city, and was intended to serve cellular, pager, and voicemail applications in the city, a restriction that was subsequently ruled impermissible by the Federal Communications Commission (FCC) while grandfathering that use in New York City. Area code 917 is also assigned to landlines predominantly in Manhattan, to relieve the shortage of numbers there.
Area codes 516 and 363 are telephone overlay area codes in the North American Numbering Plan (NANP) for the U.S. state of New York. The numbering plan area (NPA) comprises Nassau County on Long Island. Area code 516 was created in 1951 and 363 was added to the numbering plan area in 2023.
Area codes 608 and 353 are telephone area codes in the North American Numbering Plan for much of southwestern Wisconsin, including the state capital city Madison. Area code 608 was assigned in 1955 to a numbering plan area created from areas with area code 414 and area code 715, and was the third area code created in Wisconsin. Rapid growth of the area, specifically in Dane County, brought the area code close to exhaustion of central office prefixes, with NANPA projections in 2022 projecting the need for relief by late 2023. In September 2022, the Wisconsin Public Service Commission and North American Numbering Plan Administrator (NANPA) announced an overlay complex for the numbering plan area with new area code 353, with an in-service date of September 15, 2023. New central office code orders were accepted starting on July 11, 2023, but activatlon is contingent on complete exhaustion of central office codes for 608.
Area codes 813 and 656 are area codes in the North American Numbering Plan for the U.S. state of Florida in the city of Tampa, Florida, and its surrounding areas, such as Zephyrhills and Oldsmar. In 2022, due to exhaustion of central office prefixes, area code 656 was added to the service area forming an overlay complex.
Area codes 678, 470, and 943 are telephone area codes in the North American Numbering Plan (NANP) for the U.S. State of Georgia in the Atlanta metropolitan area. The area codes are assigned in an overlay plan to a combined numbering plan area (NPA) consisting of 404 and 770.
Area codes 408 and 669 are telephone area codes in the North American Numbering Plan (NANP) in the U.S. state of California. The numbering plan area comprises most of Santa Clara County and Northern Santa Cruz County, and includes Gilroy, Morgan Hill, Saratoga, Los Gatos, Monte Sereno, Milpitas, Sunnyvale, Santa Clara, Cupertino, Campbell, and San Jose.
Area codes 215, 267, and 445 are telephone area codes in the North American Numbering Plan (NANP) for Philadelphia and adjacent portions of Bucks and Montgomery counties in the U.S. state of Pennsylvania. Area code 215 was one of the original North American area codes established in 1947, while 267 and 445 are overlay codes for the same numbering plan area (NPA).
Area codes 609 and 640 are telephone overlay area codes in the North American Numbering Plan (NANP) for the central and southern parts of the U.S. state of New Jersey. The numbering plan area includes the cities of Trenton, Princeton, Ewing, Hamilton, and southeastern parts of the state and the Jersey Shore, including Atlantic City and Long Beach Island. In terms of geographic coverage, it is the largest numbering plan area in New Jersey. Area code 609 was created in a split of area code 201 in c. 1956. Area code 640 is an additional area code for the area, created on September 17, 2018.
Area code 319 is a telephone area code in the North American Numbering Plan (NANP) for the southeastern and east-central parts of the U.S. state of Iowa.
Area codes 513 and 283 are telephone area codes in the North American Numbering Plan (NANP) for the southwest of the U.S. state of Ohio, including Cincinnati and surrounding cities, such as Forest Park, Hamilton, Lebanon, West Chester, Mason, Maineville, Middletown, Milford, Norwood, Oxford, Harrison, Cleves, Miamitown and Trenton.
Area codes 816 and 975 are telephone area codes in the North American Numbering Plan (NANP) for most of the Missouri side of the Kansas City metropolitan area, the St. Joseph area, and all or part of 15 surrounding counties in northwestern Missouri. The numbering plan area originally comprised most of the northern and western two-thirds of the state, bordering with Arkansas, Illinois, Iowa, Kansas, Nebraska, and Oklahoma, but has been reduced to a ribbon bordering Kansas. 816 is one of the original 86 area codes created in 1947. The numbering plan area was converted to an overlay complex with area code 975 in 2023.
Area codes 618 and 730 are telephone area codes in the North American Numbering Plan (NANP) for southern Illinois. The numbering plan area (NPA) comprises one hundred and twenty-six municipalities, such as Carbondale, Cairo, Belleville, East St. Louis, Edwardsville, Marion, O'Fallon, Alton, Mt. Vernon, Centralia, Herrin, Salem, Metropolis, Fairview Heights, Collinsville, and Granite City. Area code 618 was one of the original North American area codes created in 1947, and 730 was added to the plan area to form an overlay complex to satisfy the need for more telephone numbers in the region. The current population of the 618/730 area code is 1,288,816 people. It encompasses approximately 15,458 square mile ; and has a population density of 83.38 people per square mile.
Area codes 503 and 971 are telephone area codes in the North American Numbering Plan (NANP) for the northwestern region of the U.S. state of Oregon. The numbering plan area (NPA) comprises the cities of Portland, Salem, and Astoria. Area code 503 was one of the original North American area codes of 1947, assigned to the entire state until 1995, when its extent was reduced to the northwestern corner. Area code 971 was assigned to the service area in stages, completed in 2008, to form an overlay in the area with ten-digit dialing.