Area codes 303 and 720

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Area codes 303 and 720 are telephone area codes serving the state of Colorado. They cover Boulder, Longmont, Aurora, Denver, Highlands Ranch and other areas in central Colorado. Area code 303 is overlayed with Area code 720, meaning that the same physical service area is served by both area codes (303 and 720) and that 10-digit dialing is required for all calls made within the service area.

Originally, all of Colorado was served by the 303 area code but as the population grew, an impending phone number shortage forced a split of the state's area codes (now into three calling areas: 303/720, 719 and 970). The area currently served by 303/720 was originally served by only the 303 area code after the Colorado area code splits. With one exception (the Roggen area, which has local calling only with itself, Brighton, and Wiggins [1]), 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 in order 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 area code, if a number appears without an area code it is assumed to be 303.