Area code 720

Area codes 303 and 720 are telephone area codes serving the north-central portion of the state of Colorado. They cover Denver, Lakewood, Littleton, Boulder, Longmont, Aurora, Castle Rock and most of the Front Range. Area code 303 is the main area code, while area code 720 is an overlay, meaning that the same physical service area is served by both area codes (303 and 720) and that ten-digit dialing is required for all calls made within the service area.

Area code 303 was one of the original area codes put into service in 1947, and originally covered the entire state of Colorado. Despite Colorado's dramatic growth during the second half of the 20th century (especially in the Denver area), it remained the sole area code in Colorado for over 40 years. By the late 1980s, an impending number shortage made a split necessary. On March 5, 1988, southeastern Colorado, including Colorado Springs and Pueblo, became area code 719. The northeastern and western portions of area code 303, including Fort Collins, Grand Junction, Vail and Aspen, switched to area code 970 on April 2, 1995, leaving area code 303 to cover its current area. With the 1995 split, 303 is the only Colorado area code that does not border another state.

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