area code 520

Area code 520 is a telephone area code in the North American Numbering Plan (NANP) for the U.S. state of Arizona. The numbering plan area comprises Tucson and most of the southeastern part of the state. Area code 520 was created in a split of area code 602 on March 19, 1995. Previously, 602 had been the sole area code for the entire state of Arizona since the introduction of area codes in 1947. Arizona's rapid growth in demand for telecommunication services during the second half of the 20th century, and the proliferation of mobile and data communication services in the 1990s required additional numbering resources. The numbering plan area originally comprised all of the state outside the Phoenix metropolitan area, but areas outside of southeastern Arizona were split again in 2001 to form area code 928 in 2001. History Area code 602 was the only area code for Arizona from the establishment of a nationwide telephone numbering plan in 1947. By the late 1980s, the state needed a second area code to satisfy population growth and increased demand for telephone numbers. Mountain Bell, the incumbent local exchange carrier in the state, requested a second area code for Arizona in 1988. BellCore, which at the time administered the assignment of area codes, denied Mountain Bell's 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, in 1990. This meant that in-state toll and collect calls would require dialing the area code. By the early 1990s, Arizona was one of the largest states served by only one area code, and it was apparent that the immediate need for a second area code could no longer be staved off. 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. 520 was introduced on 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 were then used for new telephone numbers in the Phoenix area.