Area Code Atlas

NANP-Overlay of 303 (Colorado) Numbering Plan Area (NPA) with 720 NPA

Overlay of 720 on 303 and start of 10-digit dialing

On August 31, 1998, area code 720 was overlaid on the existing 303 area code in the Denver area. This overlay required residents to begin dialing ten digits for all local calls, even for calls to neighbors. The overlay was implemented to avoid changing existing phone numbers and to provide additional numbering resources.

Mandatory 10-digit dialing for 303/720 overlay

Ten-digit dialing became mandatory in the Denver area on August 31, 1998, coinciding with the overlay of area code 720 on 303. This change was made to avoid changing existing phone numbers and to accommodate the new overlay.

NPA 720 overlay introduced on 303

Area code 720 was introduced on September 1, 1998, as an overlay to the 303 area to provide additional numbering resources in the Denver-Boulder region, requiring ten-digit dialing for all local calls.

NPA 983 relief planned for 303/720 overlay complex

The Colorado Public Utilities Commission approved the addition of area code 983 on May 21, 2021, as relief for the 303/720 overlay complex due to projected numbering exhaustion by 2023.

NPA 983 overlay on 303/720 announced

NPA 983 to Overlay NPA 303/720 (Colorado)

NPA 983 activated as overlay on 303/720

Area code 983 was activated on June 17, 2022, as an overlay to the existing 303 and 720 area codes in the Denver-Boulder area, expanding the numbering resources available to the region.