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Area codes 303 and 720 are telephone area codes serving the north-central portion of the state of Colorado. They cover Denver, Boulder, Longmont, Aurora, Castle Rock and most of the Front Range. Area code 303 is overlaid with area code 720, 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.
303 was one of the original area codes put into service in 1947, and originally covered the entire state of Colorado. However, due to Colorado's explosive growth (particularly in the Denver area) an impending number shortage made a split necessary. On March 5, 1988, southeastern Colorado received Area code 719. The northeastern and western portions of 303 switched to 970 on April 2, 1995, leaving 303 to cover its current area. 303 was overlaid with 720 on June 1, 1998.
With one exception (the Roggen area, which has local calling only with itself, Brighton, and Wiggins), the entire 303/720 area is a local calling zone, so long distance is not applied to any calls made from one phone to another within the area.
With the exception mentioned above, all users in the 303/720 area code must dial all ten digits to reach a destination phone, even if that phone is next door. Some users in the area have shortened the two area codes to a single digit with a slash for easy writing. So 303-555-1212 is written down as 3/555-1212. Since 303 is the dominant (and older) area code, if a number appears without an area code it is generally assumed to be 303.
|Colorado area codes: 303, 719, 720, 970|
|West: 970||Area code 303 / 720||East: 719|