Colo. Rev. Stat. § 40-3-108
No telephone public utility subject to articles 1 to 7 of this title shall charge or receive any greater compensation in the aggregate for the transmission of any long distance message or conversation for a shorter than for a longer distance over the same line or route in the same direction within this state, the shorter being included within the longer distance, or charge any greater compensation for a through service than the aggregate of the intermediate rates or tolls subject to articles 1 to 7 of this title. Upon application to the commission, a telephone public utility may be authorized by the commission to charge less for a longer than a shorter distance service for the transmission of messages or conversations in special cases, after investigation; and the commission may from time to time prescribe the extent to which such telephone public utility may be relieved from the operation and requirements of this section.
C.R.S. § 40-3-108