The adoption of the overlay plan, however, met with criticism from the public. In early December, 480 was assigned as the second area code. Corporation Commission staff felt the overlay offered a more long-term solution than a split, which was projected to require additional relief within four years for metro Phoenix and 12 years for suburban areas. In November 1998, on a 2–1 vote, the ACC voted to adopt the overlay for implementation in 1999. The final word rested with the Arizona Corporation Commission (ACC), which regulates public utilities. Conversely, newer entrants to the telephone market, like MCI Communications, supported a split because US West, as the dominant provider in the region, held most of the numbers in 602. The other option was a split, in which the suburban portion of the Valley would have received another area code, with 602 retained by most of the city of Phoenix. This would have required the implementation of ten-digit dialing for all local calls. US West, formerly Mountain Bell, was in favor of an overlay, in which a second area code would be added to the existing 602 area. By 1997, two ideas were on the table for relieving exchanges in metropolitan Phoenix, and the telephone industry could not reach a consensus on which was more suitable. It soon became apparent that metropolitan Phoenix, now one of the largest toll-free calling zones in the nation, needed at least one additional area code. However, Arizona's explosive population growth in the 1990s, the introduction of new competitive telephone service providers and telecommunications technologies (such as cell phones, pagers, and dial-up Internet), and an inefficient number allocation system brought 602 to the brink of exhaustion far sooner than expected. The creation of 520 was originally intended as a long-term solution under original projections, Arizona was not expected to need another area code until at least 2015. The freed central office codes in 602 were then used for new telephone numbers in the Phoenix area. The new area code became mandatory in Flagstaff, Prescott, and Yuma on June 30, 1996, and in Tucson on December 31, 1996. On that date, use of 520 became mandatory for rural Arizona. Permissive dialing of 602 continued across Arizona until October 22, 1995. In 1993, Arizona was allocated a second area code, area code 520, for all of the state outside the Phoenix metropolitan area. īy the early 1990s, the need for a new area code could no longer be staved off. This meant that in-state toll and collect calls would require dialing the area code. BellCore, which at the time administered the assignment of area codes, denied the request and instead placed Arizona into the first phase of interchangeable dialing, in which central office codes with a middle digit of 0 or 1 were made available for use. However, as early as 1988, Mountain Bell, the incumbent local exchange carrier in the state, believed Arizona was growing too quickly to remain a single numbering plan area and requested a second area code for Arizona. ĭespite Arizona's explosive population growth in the second half of the 20th century, 602 remained Arizona's sole area code for 48 years. When the American Telephone and Telegraph Company (AT&T) created the first nationwide telephone numbering plan in 1947, Arizona was designated as a single numbering plan area and received a single area code, 602, of the original 86 area codes for routing telephone toll calls between states. The creation of the three-code overlay complex made ten-digit dialing mandatory across the Valley it was already required in 480. As a result, Arizona's Corporation Commission approved a plan in 2021 to reverse the 1999 split, and convert 480 and 623 into overlay codes for the entire Phoenix area in 2023. Metro Phoenix continued to be a single rate center after the split, so that calls between the three area codes were generally local calls.īy the early 2020s, 480 and 602 were facing exhaustion within the decade, but 623 continued to have hundreds of unassigned central office codes. In 1999, a second split created the 480 NPA in the East Valley, and area code 623 in the West Valley. In 1995, the state outside metropolitan Phoenix was split off with area code 520. Under pressure from population growth and new telecommunications services, the numbering plan area (NPA) was reduced twice in five years in the 1990s. state of Arizona.Īrea code 602 is the oldest area code in Arizona and was assigned in 1947 for the entire state. Inset of the metro Phoenix area, showing the boundaries of area codes 480, 602, and 623 from 1999 to 2023, with 602 serving the middle of the present 602 area flanked by 623 to the west and 480 to the east.Īrea codes 602, 480, and 623 are telephone area codes in the North American Numbering Plan (NANP) for most of the Phoenix metropolitan area in the U.S.
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