Custer Telephone Cooperative Inc (commonly known as Custer Telephone Co-op(CTCI)) is a mobile network operator in United States assigned PLMN code 312-040 by the national telecommunications authority.

The MCC 312 identifies United States, while MNC 040 uniquely identifies this operator within the country. Together they form the PLMN (Public Land Mobile Network) identifier used by mobile devices for network selection, SIM card identification, and international roaming.

This assignment was last reported in ITU Operational Bulletin #1280 (Nov. 15, 2023). Search all MCC/MNC codes or view all United States operators .