Question: when did 10 digit dialing start in colorado

title: Area codes 303 and 720
text: 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 , reducing 303 to cover Denver and the Front Range . With the 1995 split , 303 is the only Colorado area code that does not border another state .