Published: August 02, 2021
The more densely populated area of Colorado with the city of Denver and its extensive metropolitan area (Aurora, Bolder, Lakewood, Longmont and so on) is the only area in this state using an overlay complex comprising area codes 303 and its overlay code 720 (activated in 1998).
Once again the Colorado Public Utilities Commission is planning the introduction of a relief area code for this same geographic area: the new area code 983 is to overlay 303 and 720 NPAs starting next year in June. Local calls are already being dialed using 10 digits so there will be no other changes in the way calls will be dialed after the new 983 area code's activation on June 17, 2022.
See official NANPA announcement (PDF document).