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Area codes 602, 480, and 623
Area codes 602, 480, and 623
Area codes 602, 480, and 623
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Map of area codes in Arizona, with 480, 602, and 623 highlighted in red
Area codes in Arizona and surrounding states, with the 480–602–623 overlay complex highlighted in red.
Inset of the preceding map, but showing 480, 602, and 623 as separate area codes
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.

Area 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. state of Arizona.

Area code 602 is the oldest area code in Arizona, and was assigned in 1947 for the entire state. Under pressure from population growth and new telecommunications services, the numbering plan area (NPA) was reduced twice in five years in the 1990s. In 1995, the state outside metropolitan Phoenix was split off with area code 520. In 1999, a second split created two new area codes: 480 in the East Valley and 623 in the West Valley. Metro Phoenix continued to be a single rate center after the split, so that calls between the three area codes were generally local calls.

By the early 2020s, NPAs 480 and 602 were facing exhaustion within the decade, but 623 continued to have hundreds of unassigned central office codes and was not expected to exhaust for the foreseeable future. As a result, in 2021, the Arizona Corporation Commission converted the 602, 480, and 623 numbering plan areas into an overlay complex for the entire Phoenix area by removing the involved NPA boundaries in 2023. This made ten-digit dialing mandatory across the Valley; it was already required in 480.

History

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Early history and split of 602

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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 (NPA), and received a single area code, 602, of the original 86 area codes for routing telephone toll calls into the state.[1]

602 remained Arizona's sole area code for 48 years, despite its growth in population and telecommunication services in the second half of the 20th century. However, by 1988, Mountain Bell, the incumbent local exchange carrier in the state, forecasted growth in excess of available numbering resources with exhaustion in the fourth quarter of 1990, and requested a second area code for Arizona.[2] The North American Numbering Plan Administration (Bellcore) denied the request and instead directed the use of interchangeable central office codes, in which the code has a middle digit of 0 or 1, increasing the number of possible central office codes from 640 to 792.[3][4] This meant that in-state toll and collect calls would require ten-digit dialing, including the area code.[5]

By the early 1990s, the need for a new area code could no longer be mitigated. In 1993, Arizona was allocated a second area code, area code 520, for all of the state outside the Phoenix metropolitan area.[6][7] with an in-service date of March 19, 1995. Permissive dialing of 602 continued across Arizona until October 22, 1995. On that date, use of 520 became mandatory for rural Arizona. The new area code became mandatory in Flagstaff, Prescott, and Yuma on June 30, 1996, and in Tucson on December 31, 1996. The freed central office codes in 602 became available for new allocations in the Phoenix area.[8]

Three-way split

[edit]

The creation of 520 was intended as a long-term solution. Under initial projections, Arizona was not expected to need another area code until at least 2015.[7] However, Arizona's population growth in the 1990s, along with the introduction of new competitive telephone service providers and telecommunications technologies (such as cell phones, pagers, and dial-up Internet access) brought 602 to the threshold for exhaustion mitigation much sooner than expected. It was determined that metropolitan Phoenix, now one of the largest toll-free calling zones in the nation, needed an additional area code. By 1997, two relief methodologies were discussed for providing additional resources in metropolitan Phoenix, and the telephone industry participants disagreed about the preferred configuration.[9] US West, formerly Mountain Bell, supported an overlay, in which a second area code would be added to the existing 602 area. This would have required the implementation of ten-digit dialing for all local calls. The other option was a split, in which the suburban portion of the Valley would have received a new area code, with 602 retained by most of the city of Phoenix.[9] Conversely, newer entrants to the telephone market supported a split because US West, as the dominant provider in the region, held most of the central offices in 602.[10] By October 1998, the North American Numbering Plan Administration (NANPA) declared jeopardy conservation procedures for area code 602, freezing new allocations after October 5, 1998.[11]

The decision rested with the Arizona Corporation Commission (ACC), which regulates public utilities.[10] In November 1998, the ACC voted to adopt an overlay for implementation in 1999.[12] The Corporation Commission argued that an overlay offered a longer-term solution than a split, which was projected to require additional relief within four years for metro Phoenix and twelve years for suburban areas.[13] In early December, 480 was assigned as the second area code.[14]

The adoption of the overlay plan was met with criticism from the public, because overlays were still a new concept, and required ten-digit dialing. Just two weeks after the initial vote, the ACC opted to reconsider an area code split.[15] The "doughnut" split gained two wrinkles in the process. First, the commission opted to consider placing north Phoenix in the new numbering plan area as well.[16] Second, the idea of a three-way split gained traction, in which the East Valley and West Valley areas would be removed from 602 with a new area codes each.[17]

On December 18, 1998, the Corporation Commission approved a three-way split to be effective on March 1, 1999.[18] The city of Phoenix without Ahwatukee, and areas north of Union Hills Drive remained in 602, along with slivers of Tempe and Glendale. Most of the East Valley, along with Town of Paradise Valley and north Phoenix east of 22nd Street, took area code 480. Most of the West Valley, plus all of Phoenix north of Union Hills, was placed into area code 623.[19] (556 was also considered instead of 623.[20]) The three-way split took place even though only three million phone numbers had been issued in 602, less than half of the 7.5 million numbers available.[21] Permissive dialing of the new area codes started on April 1.[22]

With the exception of the slivers of the Valley that are in the 520 and 928 numbering plan areas, no long-distance charges are applied from one portion of the Valley to another.[21][23] This makes the Valley one of the largest local calling areas in the United States; even with the split into three area codes, much of the Valley was still part of the Phoenix exchange.[24]

Boundary elimination overlay

[edit]

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 twenty years of growth. By October 2020, the NANPA forecast the exhaustion of area code 480 for the first quarter of 2024, and two years later (2026) for 602.[25] 623 exhaustion was not forecast to occur until 2069; in 2021, it had 299 assigned central office codes as opposed to more than 700 in each of 480 and 602.[26]

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. While this effectively allocated 23.4 million numbers to a service area of four million people, it would allow for pooled numbers to be used anywhere in the metropolitan area and for the assignment of new numbers (primarily from 623, as it had most of the unassigned codes) throughout the single rate center. By this time, overlays had become the standard for relief. No area codes had been split anywhere in the United States since 2007,[27] and it was not possible to split the 480 area code because of the 2021 implementation of 10-digit dialing there.[26]: 5–6 [a] This would save the assignment of two area codes compared to individual all-service distributed overlays of 480 and 602 and last 26 years, as opposed to 35 for the introduction of new area codes.[26] The Corporation Commission approved this plan on November 9, 2021. Implementation began in August 2022, after the national deadline to activate 988. 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. As ten-digit dialing had already been in use in 480, 520, and 928, the boundary elimination made it mandatory statewide.[29][30]

See also

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Notes

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References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Area codes 602, 480, and 623

View on Grokipedia
from Grokipedia
Area codes 602, 480, and 623 are area codes in the (NANP) serving the in Maricopa County and portions of Pinal County in the U.S. state of . These codes collectively cover a rapidly growing urban region that includes major cities such as Phoenix, Scottsdale, Mesa, Tempe, Chandler, Gilbert, Glendale, Peoria, and Avondale, as well as surrounding suburbs and communities like Sun City, Buckeye, and Cave Creek. Originally distinct in their geographic boundaries, the codes now operate as an overlay complex following a boundary elimination approved in to address number exhaustion, requiring 10-digit local dialing throughout the region since August 2023. The foundational code, 602, was established in 1947 as one of the original 86 area codes created by the and initially served the entire state of . Due to Arizona's population boom in the late , particularly in the Phoenix area, 602 was split on March 19, 1995, to create area code 520 for southern and outside the Phoenix metro, leaving 602 for the central region. Further growth necessitated another division on March 1, 1999, when 602 was split into three codes: 602 retained for central Phoenix and adjacent areas; 480 assigned to the east and south-central suburbs including Scottsdale, Mesa, Tempe, Chandler, and Gilbert; and 623 allocated to the west and northwest including Glendale, Peoria, Avondale, and Sun City. To conserve numbering resources amid continued expansion— with projections showing exhausting by early and 602 by mid-2026—the approved a boundary elimination overlay on November 2, 2021 (Decision No. 78311), merging the service areas of 480, 602, and 623 into a single overlay for the entire Phoenix metro. This change eliminated geographic boundaries between the codes, allowing all three to be used interchangeably across the region, and introduced permissive 10-digit dialing on February 11, 2023, which became mandatory on August 12, 2023, for all local calls within the overlay to prevent disruptions from number shortages. The overlay ensures long-term availability of numbers in this economically vital area, home to over 5.1 million residents as of and a hub for , , and industries.

Overview

Current Coverage and Scope

Area codes 602, 480, and 623 collectively serve the entire through a boundary elimination overlay established in 2023, encompassing all of Maricopa County and portions of Pinal County in . This unified structure means that the three codes are interchangeable across the region, with no distinct geographic assignments for individual codes. The primary cities covered include central, eastern, and western portions of Phoenix; Mesa; Scottsdale; Tempe; Chandler; Gilbert; Glendale; Peoria; Surprise; Avondale; Goodyear; Buckeye; Apache Junction; and Fountain Hills. Additional communities served are El Mirage, Guadalupe, Litchfield Park, Paradise Valley, Queen Creek, Sun City, Tolleson, and Youngtown. This coverage aligns with the Phoenix-Mesa-Scottsdale , supporting residential, commercial, and governmental telecommunications needs throughout the urban and suburban expanse. As of 2024, the population served by these area codes is estimated at approximately 5.2 million residents, reflecting the metro area's rapid growth and high demand for telephone numbers. Areas outside this metro region, such as Tucson (served by ) and northern Arizona (served by ), are explicitly excluded from this coverage.

Activation Dates and Numbering Status

Area code 602 was activated in October 1947 as Arizona's original numbering plan area, initially covering the entire state. Area code 480 was introduced on March 1, 1999, serving the east suburbs as part of a three-way split of 602 to address growing demand. Area code 623 was similarly introduced on March 1, 1999, for the west suburbs during the same split. In September 2023, a boundary elimination overlay took effect, creating a full overlay complex where 602, 480, and 623 are interchangeable across the to maximize numbering resources. As of November 2025, all three codes operate in this overlaid configuration, with 10-digit dialing required for local calls. Area code 602 is nearing central office code exhaustion, projected for the second quarter of without relief, but the overlay allows supplementation from the other codes to meet demand. In contrast, and 623 maintain remaining central office code capacity, supporting ongoing assignments. projections indicate that the 2023 boundary elimination avoided the earlier forecasted exhaustion of in the first quarter of 2024, with continuous monitoring of the entire complex for potential future relief planning.

Historical Development

Establishment and Early Expansion of 602 (1947–1995)

Area code 602 was established on October 6, 1947, as part of the original (NANP) developed by and the to enable direct-distance dialing across the , , and parts of the . It was one of 86 initial codes assigned to cover the continental and , with 602 designated for the entire state of due to its relatively low population of 499,261 as recorded in the 1940 census. This assignment reflected the NANP's design to allocate single codes to low-density states, prioritizing ease of use on telephones where middle digits of 0 or 1 allowed for efficient routing. In its early years, area code 602 primarily served the state's two largest cities, Phoenix and Tucson, where most telephone infrastructure was concentrated amid Arizona's rural character. Telephone service expanded gradually, supporting local exchanges in these urban centers while rural areas relied on manual switchboards or party lines. Post-World War II economic and demographic shifts accelerated growth, particularly in the , fueled by the establishment of military bases during the war, the invention of affordable residential in the late , and migration drawn to the region's climate and job opportunities in and defense. By 1950, Arizona's population had risen to 749,587, with Phoenix's metro area experiencing a surge that increased demand for telephone lines and prompted infrastructure investments by the Arizona Public Service Company and local exchanges. For nearly five decades, 602 functioned as Arizona's sole area code, encompassing all geographic areas without splits or overlays as the state's transitioned from and to suburban development. This statewide coverage persisted through the and , accommodating steady telephone penetration rates that reached over 90% of households by the early . However, explosive in the Phoenix metro—where tripled in Maricopa County alone—drove unprecedented demand, with Arizona's total climbing to 3,665,228 by the 1990 and further to 4,432,499 by mid-1995. By the early , this growth had exhausted significant portions of available central office codes within 602, necessitating relief planning to avert full numbering resource depletion.

1995 Split with Area Code 520

The creation of area code 520 was announced in 1994 by the North American Numbering Plan Administration to provide relief for Arizona's existing area code 602, which had covered the entire state since 1947 and was facing resource constraints due to rapid population and telephone demand growth. This geographic split, rather than an overlay, was selected to efficiently allocate numbering resources by isolating lower-growth regions from the high-demand Phoenix metropolitan area. Area code 520 entered service on March 19, 1995, serving Tucson, , and much of the state's rural areas outside Maricopa County. Existing customers in these regions were assigned the new code, while 602 was retained for the Phoenix metro and adjacent northern areas; a permissive dialing period allowed both area codes to be used interchangeably for several months to ease the transition for callers. The split affected telephone lines across a vast expanse, primarily in lower-density areas with slower growth rates, thereby preserving central office codes in 602 for the state's primary urban hub. The rationale centered on projections of statewide numbering exhaustion in 602 by the late 1990s, driven by Arizona's overall expansion but concentrated in the Phoenix region. By carving out the slower-growing south and rural zones into 520, the plan conserved resources for high-growth northern areas, postponing further relief needs in 602 until additional measures were required. Post-split, 602's scope was confined to central and northern Arizona, laying the groundwork for subsequent Phoenix-specific adjustments amid continued urban development pressures.

1999 Three-Way Split of 602

In 1998, the approved a three-way split of the remaining area code 602 to address growing demand in the , with the change becoming effective on March 1, 1999. This division created area code 480 to serve the East Valley and area code 623 to serve the West Valley, while retaining 602 for the central core of Phoenix. The split built upon the relief provided by the 1995 creation of for southern and . The geographic boundaries were drawn to divide the Phoenix rate center along key lines, with area code 480 assigned to areas generally east of Central Avenue, encompassing cities such as Mesa, Scottsdale, Tempe, Chandler, and Gilbert. Area code 623 covered areas to the west and northwest, including Glendale, Avondale, Buckeye, Sun City, and Tolleson. Area code 602 was preserved for the inner portions of Phoenix, including much of downtown and surrounding central neighborhoods like Ahwatukee and parts of Cave Creek. To facilitate the transition, a permissive period for 10-digit dialing began on January 25, 1999, allowing callers to use either 7-digit or 10-digit formats for local calls; this period ended on October 23, 1999, after which 10-digit dialing became mandatory for calls between the new area codes. The split served a Phoenix metropolitan population of approximately 3 million people and averted the immediate exhaustion of available numbers in 602 amid rapid growth driven by the wireless telephone boom. The plan received approval from the on December 18, 1998, in coordination with the Administrator () and under oversight as part of NANP-wide conservation efforts.

2023 Boundary Elimination Overlay

In response to projected number exhaustion in the 480 numbering plan area (NPA) by the first quarter of 2024, the (ACC) approved a boundary elimination overlay relief plan on November 2, 2021, via Decision No. 78311. This plan eliminated the geographic boundaries between the , 602, and 623 NPAs that had been in place since the 1999 three-way split of the original 602 area code, unifying them into a single overlay complex serving the entire Phoenix metropolitan region. Rather than introducing a new area code, the overlay pooled available numbering resources across all three codes to address the shortage without disrupting existing service. The implementation occurred in phases, beginning with permissive 10-digit local dialing on February 11, 2023, for the 602 and 623 NPAs, while the NPA had already required 10-digit dialing since 2021. Mandatory 10-digit dialing—requiring callers to dial the full area code plus seven-digit phone number for all local calls—took effect on August 12, 2023, across the entire overlay region. Under the new structure, service providers can assign new numbers from any of the three area codes (, 602, or 623) regardless of the customer's physical location within the unified territory, promoting more efficient . Existing phone numbers remained unchanged, and no customer action was required beyond adapting to 10-digit dialing. This boundary elimination affected approximately 5 million telephone lines in the Phoenix metro area, one of the fastest-growing regions in the North American Numbering Plan (NANP). By removing service boundaries, the plan extended the usability of the existing codes, with projections indicating relief until at least the mid-2030s, while aligning with national requirements for 10-digit dialing to support emergency services like the 988 Suicide & Crisis Lifeline. As of October 2024 NANPA projections, the overlay has postponed exhaustion beyond 2030. The change marked a novel application of boundary elimination as an alternative to traditional overlays or splits in the NANP.

Geographic and Administrative Context

Phoenix Metropolitan Area Boundaries

The region served by area codes 602, 480, and 623 encompasses the , which includes all of Maricopa County—with a 2024 population of 4,673,096—and portions of Pinal County. This metropolitan area spans approximately 14,569 square miles of arid desert landscape, featuring a diverse urban structure with 27 incorporated cities and towns, centered around Phoenix as the primary hub. The physical and administrative boundaries extend north to the vicinity of Black Canyon City and Daisy Mountain, south to Maricopa and San Tan Valley, east to the , and west to Harquahala Valley, aligning with the combined county perimeters that define the region's scope. These area codes provide coverage for this metropolitan zone, excluding overlap with , which serves the Tucson metropolitan area, and , which covers Flagstaff and northwestern Arizona. Following the 2023 boundary elimination, visual maps depict a single, unified service area for all three codes across the entire region.

Population Growth and Demand Drivers

The Phoenix metropolitan area's has expanded significantly since the mid-20th century, growing from approximately 375,000 residents in 1950 to about 5.2 million in 2025 (as of mid-2025 estimate), with an average annual growth rate of approximately 3.4% over that period, though recent years (2020-2024) have seen rates around 1.5%. This sustained increase, fueled by domestic and alongside economic opportunities such as the tech boom, has placed considerable pressure on infrastructure, including the allocation of numbers in area codes 602, 480, and 623. Key historical drivers include post-World War II suburbanization, which more than doubled the population in the 1950s through developments and widespread adoption of , enabling rapid . The 1980s boom, characterized by speculative investment and expansion, further intensified growth, while the 2000s housing surge—adding over 900,000 residents between 2000 and 2010—directly contributed to heightened demand for additional area codes. These trends transformed the region from a modest urban center into a major hub, necessitating splits to accommodate rising telephone number needs. In the , migration from high-cost states like accelerated growth, drawn by expanding tech sectors in Scottsdale and Chandler, where companies established operations and created thousands of jobs. The amplified this through shifts, spurring a surge in the west Valley; for instance, Buckeye's population grew by 48% from 2018 to 2023 as families sought affordable suburban options. Consequently, lines now comprise over 70% of total numbers in the area, reflecting broader shifts toward mobile usage and intensifying exhaustion risks. Projections estimate the metro population will reach 6 million by 2030, driven by continued migration and job growth, requiring vigilant monitoring of numbering resources. Economically, the region ranks as the 10th-largest U.S. metro area, with semiconductors—a sector anchored by Intel's Chandler —playing a pivotal role in attracting workers and elevating telecom demands through data-intensive operations and supply chain expansions.

Technical Implementation

Overlay Mechanics and Number Exhaustion

In the (NANP), an overlay assigns multiple numbering plan area (NPA) codes—specifically 602, 480, and 623—to the same geographic region, enabling telecommunications carriers to assign numbers from any of these codes without regard to prior boundaries, thereby extending the overall numbering capacity for the . This structure contrasts with geographic splits, as it preserves existing customer numbers while distributing new assignments flexibly across the shared pool. Each NPA supports up to 792 central office codes (NXX prefixes), each providing 10,000 telephone numbers, for a total potential of 7.92 million numbers per code, though actual availability is reduced by administrative reservations and unused blocks. By late 2021, the 480 NPA had reached high utilization levels, with the Administrator () projecting exhaustion of its central office codes by the first quarter of 2024, driven by and increased demand for mobile and VoIP services in the region. Similarly, the 602 NPA was forecasted to exhaust by the second quarter of 2026, while 623 remained more stable. Number resource management involves carriers submitting requests to for new central office codes based on projected needs, with assignments now occurring across the unified 480/602/623 overlay following the boundary elimination implemented on , 2023, to balance load and prevent premature exhaustion in any single code. This post-overlay approach disregards legacy geographic restrictions, allowing efficient allocation regardless of the specific location within the Phoenix rate center. To conserve resources, measures such as rate center consolidation have been employed, merging smaller or overlapping rate centers to reduce the number of required code assignments per carrier and optimize the shared pool across the overlay. No further geographic splits or new NPAs are planned unless all three codes approach simultaneous exhaustion, as the overlay design defers such actions. Recent forecasts as of October 2025 indicate that the combined capacity of the 480/602/623 overlay will suffice well beyond 2035, with projections extending to the 2040s under current demand trends, thanks to the boundary elimination and ongoing conservation efforts. The Arizona Corporation Commission continues to monitor utilization through industry reports and data to ensure timely adjustments if growth accelerates.

Dialing Changes and Customer Impact

Prior to the 2023 overlay implementation, dialing procedures in the varied by area code. Customers within the 602 or 623 area codes could use 7-digit dialing for local calls to other numbers in the same code, while calls crossing into the area code required 10 digits, including the area code. In contrast, the area code had already mandated 10-digit dialing for all local calls since October 24, 2021, in response to the FCC's requirement to implement the lifeline. The boundary elimination overlay introduced significant changes to standardize dialing across the region. A permissive period for 10-digit dialing began on February 11, 2023, allowing customers in the 602 and 623 area codes to optionally use 10 digits for local calls while 7-digit dialing remained functional. This transitioned to mandatory 10-digit dialing for all local calls throughout the 480, 602, and 623 regions starting August 12, 2023, with calls using only 7 digits resulting in an prompting the addition of the area code. The full elimination of geographic boundaries between the codes took effect on September 12, 2023, enabling uniform service across the combined area. These changes had minimal disruption for most users, as existing telephone numbers remained unchanged and local call rates stayed the same. However, new telephone services or additional lines activated after September 12, 2023, could be assigned any of the three area codes regardless of the customer's specific location within the region. Customers were advised to update personal contact lists, auto-dialers, and integrated systems like to accommodate 10-digit entries. Businesses and organizations experienced varied effects depending on their telephony setup. Voice over Internet Protocol (VoIP) and mobile services were largely unaffected in terms of functionality, as these systems typically support 10-digit dialing natively and required no hardware changes. Traditional landline users, particularly those with older equipment such as multi-line business phones or alarm systems, often needed to reprogram or upgrade devices to prevent failed calls during the transition. No mandatory number changes were required, but businesses were encouraged to revise websites, stationery, and advertising materials to reflect the new dialing protocol. To facilitate the transition, extensive public education campaigns were launched by the (FCC), the (ACC), and telecommunications carriers starting in early 2023. The FCC provided general guidance on area code relief plans, while carriers like distributed notices via mail, , and billing inserts from February 2023 onward, emphasizing the permissive period and mandatory deadline. The ACC coordinated regional awareness efforts, including a dedicated webpage and (602-542-4251) for inquiries, to ensure customers understood that the changes preserved without altering 911 access or toll charges.

References

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