Telephone area codes 602, 480, and 623 in the North American Numbering Plan (NANP) cover most of the Phoenix metropolitan area in the U.S. state of Arizona, including the city of Phoenix and the vast majority of its suburbs.
Area code 602 is the oldest of the three and was assigned in 1947 as the only area code for the entire state of Arizona. Under pressure from a population boom and new telecommunications services, it was split twice in five years in the 1990s. The first split in 1995 cleaved off numbers outside of metropolitan Phoenix to form area code 520 (since split itself to form 928); the second split, in 1999, carved out area codes 623 in the West Valley and 480 in the East Valley, with most of the city of Phoenix itself remaining in 602. The 1999 split had originally been proposed and approved as an overlay of a second area code, but the Arizona Corporation Commission nearly immediately reconsidered, leading to the adopted split. Metro Phoenix was consolidated into one rate center, so calls between the three area codes were generally local calls.
By the early 2020s, 480 and 602 were facing exhaustion within the decade, but 623 continued to have hundreds of unassigned central office codes. As a result, in 2021, the Corporation Commission approved a plan to convert the 1999 split into a three-code overlay complex beginning in 2023 instead of assigning two new overlay codes in the 480 and 602 areas within three years. This resulted in a transition to mandatory ten-digit dialing in the previous 602 and 623 areas; it was already required in 480.
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