North American area code 623 is a state of Arizona telephone area code serving most of the western portion of the Phoenix metropolitan area. It was created in a split from area code 602 on April 1, 1999, when it was evident that the Valley of the Sun was expanding too rapidly to remain in one area code. Generally, the West Valley and the outer northwestern suburbs became 623, the eastern suburbs and the Phoenix neighborhood of Ahwatukee became area code 480, and inner Phoenix remained in 602.
623 covers areas including Glendale (except the section north of the Arizona Canal and south of Union Hills, which remained in 602), Peoria (except northwest near Vistancia and Lake Pleasant, which is in 928), Sun City, Sun City West, El Mirage, Surprise, Youngtown, Avondale, Cashion, Tolleson, Goodyear, and Buckeye, as well as some of western Phoenix, specifically the city north of Union Hills and west of the 2000 E Grid, south of the Arizona Canal from 43rd Ave to 39th Ave, west of 39th Ave from the Arizona Canal south to Maryland Ave, along 43rd Ave from Maryland to Indian School, diagonally southwest from 43rd Ave & Indian School to 63rd Ave & Interstate 10, then south along 63rd Ave to the Salt River and then the Gila River Indian Reservation. The 602/623 boundary runs roughly diagonally through northern Glendale.