Idaho Code § 62-803
It is the purpose of this chapter, among other things, to require cooperation on the part of telegraph and telephone companies in the transmission of messages and communications to or from any place where the use of both means of communication is necessary or desirable and where such use will expedite the transmission of any such message or communication; and it shall be unlawful for any telegraph or telephone company or any person having charge of any public telegraph or telephone service or system, controlling or operating any such system within this state, in whole or in part, or any employee thereof, to transmit any message or communication upon which the fees and charges have been paid, tendered or offered, as herein provided, by mail, over any portion of the distance over which such message or communication is to be transmitted, unless neither telegraph nor telephone service is available, and then such means of transmission shall only be used for such distance as necessary in conveying such message to the nearest telegraph or telephone station.
Idaho Code § 62-803