Area code 602

602 is one of the original area codes established in October 1947 and originally covered the entire state of Arizona. By the late 1980s, Arizona's explosive population growth in the second half of the 20th century led to analysis of the feasibility of a second area code in the state. Mountain Bell, the incumbent local exchange carrier in the state, requested a second area code for Arizona in 1988.[1] BellCore, which at the time administered the assignment of area codes, denied Mountain Bell's request and instead allowed the state to go to the first phase of interchangeable dialing, in which central office codes with a middle digit of 0 or 1 were made available for use, in 1990.[2] This meant that in-state toll and collect calls would require dialing the area code.[3]

By the early 1990s, Arizona was one of the largest states served by only one area code. In advance of the 1995 introduction of interchangeable area codes (area codes with a middle digit not 0 or 1), and in response to continued population growth, Arizona was allocated a second area code, area code 520. The new area code completely surrounded metropolitan Phoenix, which mostly retained 602.[4] 520 was introduced on March 19, 1995, and after an extended permissive dialing period, mandatory use of the new area code to reach outstate Arizonans was phased in during 1995 and 1996; the freed central office codes in 602 were then used for new telephone numbers in the Phoenix area.[5]

Arizona's explosive population growth in the 1990s, the introduction of new competitive telephone service providers and telecommunications technologies, and inefficient practices for the assignment of telephone numbers meant that an area code split designed to last the state 20 years[4] only worked for four. It soon became apparent that metropolitan Phoenix needed at least one additional area code. By 1997, two ideas were on the table for how to introduce a second area code into metropolitan Phoenix, and the telephone industry could not reach a consensus on which was more suitable.[6] US West, formerly Mountain Bell, was in favor of an overlay. In an overlay, a second area code would be added to the existing 602 area. This requires the implementation of ten-digit dialing for all local calls. US West preferred this to a split—in which the suburban portion of 602 would be allotted another area code, with 602 retained by areas primarily in the city of Phoenix.[6] Conversely, newer entrants to the telephone market, like MCI Communications, supported a split because US West, the dominant competitor, held most of the numbers in 602.[7]

The final word rested with the Arizona Corporation Commission (ACC), which regulates public utilities.[7] In November 1998, on a 2–1 vote, the ACC voted to adopt the overlay for implementation in 1999.[8] 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.[9] In early December, 480 was assigned as the second area code.[10]

The adoption of the overlay plan, however, met with criticism from the public. Overlays were still a new concept at the time and met with some resistance due to the need for ten-digit dialing. Just two weeks after voting in favor, the ACC opted to reconsider in a move that clearly favored the adoption of a split.[11] The "doughnut" split gained two wrinkles in the process. First, the commission opted to consider putting north Phoenix in the new area code as well.[12] Second, the idea of changing to a three-way split where the East Valley and West Valley areas being spun out from 602 would receive their own prefixes gained traction.[13]

On December 18, 1998, the Corporation Commission approved the final plan to go into effect on September 1, 1999: a three-way split, under which the city of Phoenix minus Ahwatukee and areas north of Union Hills Road remained in 602; the East Valley, Town of Paradise Valley, and north Phoenix east of 22nd Street took area code 480; and the West Valley was placed into area code 623.[14] (556 was also considered instead of 623.[15]) All calls remained local across all three new area codes. The three-way split took place even though, in actuality, just three million phone numbers had been issued from the 7.5 million available in 602.[16] Permissive dialing of the new area codes started on April 1.[17]

The three Valley area codes form one of the largest local calling areas in the western United States. With few exceptions, no long-distance charges are applied from one portion of the Valley to another. Even after the split into three area codes, most of the Valley is still part of the Phoenix exchange, making Phoenix one of the largest rate centers in the United States.[18]

The three-way split, combined with the implementation of number pooling and other practices to encourage efficient use of telephone numbers, gave the Valley enough telephone numbers to absorb more than 20 years of growth. 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.[19] However, 623 was not forecast to exhaust until 2069; in 2021, it had 299 assigned central office codes as opposed to more than 700 in each of 480 and 602.

After NANPA initiated relief planning for 480, the state's telecommunications industry recommended to the Arizona Corporation Commission that the 1999 area code boundaries be eliminated, creating a three-code overlay complex and allowing the assignment of new numbers (primarily from 623) throughout the Phoenix rate center. This would save the assignment of two area codes and last 26 years, as opposed to 35 for the introduction of new area codes.[20] The Corporation Commission approved this plan on November 9, 2021. Implementation would not begin until August 2022, after the national deadline to activate 988, with a six-month permissive 10-digit dialing period for the 602 and 623 areas to begin on February 11, 2023, ahead of the overlay becoming effective in August of that year.[21][22]