| Lynnville Telephone Company, Inc. | - | Sully, IA | Active |
| M&L Enterprises, Inc. | Skyline Telephone Co. | Mt Vernon, OR | Inactive |
| MGW Telephone Company, Inc. | - | Staunton, VA | Active |
| MTC Wireless, LLC. | - | Madison, WI | Inactive |
| Mabel Cooperative Telephone Company | - | Mabel, MN | Active |
| Madison County Telephone Co., Inc. | Madison County Telephone Company, Inc. | Huntsville, AR | Active |
| Madison Tel. Co. | Madison Telephone Company | Staunton, IL | Active |
| Madison Tel. Co. Inc. | Madison Telephone LLC | Madison, KS | Active |
| Magazine Tel. Co. | Magazine Telephone Company | Magazine, AR | Active |
| Magna5 RTC LLC | Richmond Telephone Company | Plano, TX | Active |
| Mahanoy & Mahantango Tel. Co. | TDS Telecom | Madison, WI | Active |
| Malheur Home Telephone Company | Qwest Corporation | Denver, CO | Inactive |
| Manawa Tel. Co. Inc. | Manawa Telephone Company, Inc. | Wisconsin Rapids, WI | Active |
| Manchester-Hartland Tel. Co. | Manchester-Hartland Telephone Company | Manchester, MN | Active |
| Manilla Tel. Co. | Manilla Telephone Company | Harlan, IA | Inactive |
| Manti Telephone Co. Inc. | Manti Telephone Company | Manti, UT | Active |
| Margaretville Tel. Co. Inc. | Margaretville Telephone Company, Inc. | Margaretville, NY | Active |
| Marianna & Scenery Hill Tel. Co. | Marianna & Scenery Hill Telephone Company | Mattoon, IL | Active |
| Mark Twain Rural Tel. Co. | Mark Twain Rural Telephone Company | Hurdland, MO | Active |
| Marne & Elk Horn Tel. Co. | Marne & Elk Horn Telephone Company | Elk Horn, IA | Active |
| Marquette-Adams Telephone Cooperative, Inc. | - | Oxford, WI | Active |
| Martelle Coop. Tel. Assn. | Martelle Cooperative Telephone Association | Martelle, IA | Active |
| Mashell Telecom, Inc. | Rainier Group | Eatonville, WA | Active |
| Massena Tel. Co. | Massena Telephone Company | Massena, IA | Active |
| Matanuska Tel. Assn. Inc. | Matanuska Telephone Association, Inc. | Palmer, AK | Active |
| McClellanville Telephone Co. | TDS Telecom | Madison, WI | Active |
| McClure Tel. Co. | McClure Telephone Company | McClure, OH | Active |
| McDaniel Telephone Company | TDS Telecom | Madison, WI | Active |
| McDonald County Tel. Co., Inc. | McDonald County Telephone Company | Pineville, MO | Active |
| McDonough Telephone Cooperative | - | Colchester, IL | Active |
| McLoud Telephone Company | - | Oklahoma City, OK | Active |
| McNabb Telephone Company | - | McNabb, IL | Active |
| MebTel, Inc. | Mebtel Communications | Monroe, LA | Active |
| Mechanicsville Tel. Co. | Mechanicsville Telephone Company | Mechanicsville, IA | Active |
| Mediapolis Tel. Co. | Mediapolis Telephone Company | Mediapolis, IA | Active |
| Medicine Park Tel. Co. | Medicine Park Telephone Company | Medicine Park, OK | Active |
| Melrose Tel. Co. | Melrose Telephone Company | Perham, MN | Active |
| Merchants & Farmers Telephone Company | TDS Telecom | Madison, WI | Active |
| Merrimack County Tel. Co. | TDS Telecom | Madison, WI | Active |
| Mescalero Apache Telecom Inc. | Mescalero Apache Telecom | Mescalero, NM | Active |
| Metamora Tel. Co. | Metamora Telephone Company | Metamora, IL | Active |
| Michigan Bell Telephone Company | AT&T Michigan | Detroit, MI | Active |
| Michigan Central Broadband Company | - | Carney, MI | Active |
| Micronesian Telecommunications Corporation | Micronesian Telecomm. Corp. Northern Mariana Is. | Saipan, MP | Active |
| Mid Century Tel. Coop. Inc. | Mid-Century Telephone Co-Operative, Inc. | Fairview, IL | Active |
| Mid-America Telephone Co. | TDS Telecom | Madison, WI | Active |
| Mid-Maine Telecom LLC | - | Oneonta, AL | Active |
| Mid-Maine Telecommunications | Mid-Maine Telecom | Bangor, ME | Inactive |
| Mid-Plains Rural Tel. Co-op. Inc. | Mid-Plains Rural Telephone Cooperative, Inc. | Tulia, TX | Active |
| Mid-Plains Telephone, LLC | TDS Telecom | Madison, WI | Active |