Area code 720 is the telephonearea code serving the state of Colorado. It covers Boulder, Longmont, Aurora, Denver and other areas in central Colorado. It overlays with Area code 303. The telephone or phone (Greek: tele = far away and phone = voice) is a telecommunications device which is used to transmit and receive sound (most commonly voice and speech) across distance. ... A telephone numbering plan is a system that allows subscribers to make and receive telephone calls across long distances. ... Official language(s) English Capital Denver Largest city Denver Area Ranked 8th - Total 104,185 sq mi (269,837 km²) - Width 280 miles (451 km) - Length 380 miles (612 km) - % water 0. ... In geology, a boulder is a rock with grain size of more than 256 mm (10 inches) diameter. ... Longmont is a city located in Boulder County, Colorado. ... Look up Aurora, aurora in Wiktionary, the free dictionary. ... This article refers to the state capital of Colorado. ... Area code 303 is the telephone area code serving the state of Colorado. ...