Santel Communications Cooperative (OCN 1676) has had company-wide local calling since some time in 2014. They previously had optional local calling plans where subscribers could choose to pay a monthly fee to call specified exchanges.
Updated local calling information for Interstate Telephone Cooperative/Stockholm-Strandburg Telephone Company (OCN 1651, 1654, and 1679)
Dakota Central Telecommunications (OCN 1610 and 1683) has company-wide local calling – not sure when this took effect. Source: DCT
Dickey Rural Networks (OCN 1611) also has company-wide local calling as of 2013-12-01. Source: DRN
Farmers Mutual Telephone Company (OCN 1389 and 2836) and Federated Telephone Cooperative (OCN 1390, 1403 and 2629) have formed a partnership known as Acira, with company-wide local calling among members of both companies. Source: Acira