Under pressure from population growth and new telecommunications services, the numbering plan area (NPA) was reduced twice in five years in the 1990s.
As a result, the Arizona Corporation Commission, which regulates public utilities, approved a plan in 2021 to reverse the 1999 split and convert 602, 480, and 623 into overlay codes for the entire Phoenix area in 2023.
[5] 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.
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.
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.
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.
[7] 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.
[14] On December 18, 1998, the Corporation Commission approved the final plan to go into effect on September 1, 1999: a three-way split.
The city of Phoenix minus Ahwatukee and areas north of Union Hills Drive remained in 602, along with slivers of Tempe and Glendale.
By October 2020, the North American Numbering Plan Administrator (NANPA) forecast that area code 480 would be exhausted by the first quarter of 2024 and 602 two years later in 2026.
[22] After NANPA initiated relief planning for 480, the state's telecommunications industry recommended to the Corporation Commission that the 1999 area code boundaries be eliminated, creating a three-code overlay complex.
A six-month permissive ten-digit dialing period for the 602 and 623 areas commenced on February 11, 2023, ahead of the in-service date of September 12, 2023, of the overlay.