| Mid-Rivers Telephone Cooperative, Inc. | - | Circle, MT | Active |
| Mid-State Telephone Co. | TDS Telecom | Madison, WI | Active |
| Middle Point Home Tel. Co. | The Middle Point Home Tel. Co. | Wapakoneta, OH | Active |
| Midstate Communications Inc. | Midstate Communications, Inc. | Stanley, ND | Active |
| Midstate Communications, Inc. | - | Kimball, SD | Active |
| Midstate Tel. Co. | Midstate Telephone Company | Stanley, ND | Active |
| Midvale Telephone Company | MTE Communications | Midvale, ID | Active |
| Midway Tel. Co. | Midway Telephone Company | Munsing, MI | Active |
| Midway Telephone Co. | TDS Telecom | Madison, WI | Active |
| Midwest Telephone Co. | - | Perham, MN | Active |
| Miles Coop. Tel. Assn. | Miles Cooperative Telephone Association | Miles, IA | Active |
| Miller Telephone Co. | - | Ventura, IA | Inactive |
| Miller Telephone Co. Inc. - MO | Miller Telephone Company | Miller, MO | Active |
| Millington Tel. Co. Inc. | Millington Telephone Company, Inc. | Jonesboro, AR | Active |
| Millry Telephone Co., Inc. | Millry Telephone Company, Inc. | Millry, AL | Active |
| Milltown Mutual Tel. Co. | Milltown Mutual Telephone Company | Milltown, WI | Inactive |
| Minburn Tel. Co. | Minburn Telephone Company | Minburn, IA | Active |
| Minburn Telecommunications, Inc. | - | Woodward, IA | Active |
| Minerva Valley Tel. Co. Inc. | Minerva Valley Telephone Company, Inc. | Zearing, IA | Active |
| Minford Telephone Company | - | Minford, OH | Active |
| Minnesota Lake Telephone Company | BEVCOMM | Blue Earth, MN | Inactive |
| Minnesota Valley Telephone Company | - | Franklin, MN | Active |
| Missouri Valley Communications, Inc. | - | Scobey, MT | Active |
| Moapa Valley Tel. Co. | Moapa Valley Telephone Company | Overton, NV | Active |
| Modern Coop. Tel. Co. | Modern Cooperative Telephone Company | South English, IA | Active |
| Modern Telecommunications Company | - | Green City, MO | Inactive |
| Mokan Dial, Inc. | - | MACCLENNY, FL | Active |
| Molalla Tel. Co. | Molalla Communications Company | Molalla, OR | Active |
| Mon-Cre Tel. Coop. Inc. | Mon-Cre Telephone Cooperative, Inc. | Ramer, AL | Active |
| Monitor Coop. Tel. Co. | Monitor Cooperative Telephone Company | Woodburn, OR | Active |
| Monon Tel. Co. Inc. | Monon Telephone Company, Inc. | Monon, IN | Active |
| Monroe Telephone Company | - | Monroe, OR | Active |
| Montrose Mutual Tel. Co. | Montrose Mutual Telephone Company | Louisville, IL | Active |
| Moore & Liberty Telephone Company | Moore & Liberty Telephone Co. | Enderlin, ND | Inactive |
| Mosinee Tel. Co. | TDS Telecom | Madison, WI | Active |
| Mosinee Telecom, LLC. | - | Madison, WI | Inactive |
| Moultrie Independent Telephone Company | - | Lovington, IL | Active |
| Mound Bayou Tel. and Communications Inc. | Mound Bayou Telephone & Communications Corporation | Bay Springs, MS | Active |
| Moundridge Tel. Co. | The Moundridge Telephone Company, Inc. | Moundridge, KS | Active |
| Moundville Telephone Company | Moundville Telephone Company, Inc. | Moundville, AL | Active |
| Mountain Rural Tel. Coop. Corp. Inc. | Mountain Telephone | West Liberty, KY | Active |
| Mountain View Tel. Co. | Mountain View Telephone Co. | Mountain Home, AR | Active |
| Mt. Angel Tel. Co. | Mt. Angel Telephone Company | Mt Angel, OR | Active |
| Mt. Horeb Tel. Co. | Mount Horeb Telephone Co. | Mount Horeb, WI | Active |
| Mt. Rushmore Tel. Co. | Mount Rushmore Telephone Company | Clara City, MN | Inactive |
| Mt. Vernon Telephone Co. | TDS Telecom | Madison, WI | Active |
| Mud Lake Telephone Cooperative Assn. Inc. | Mud Lake Telephone Cooperative Assn., Inc. | Dubois, ID | Active |
| Muenster Tel. Corp. of Texas | Nortex Communications | Muenster, TX | Active |
| Mukluk Tel. Co. Inc. | Mukluk Telephone Company | Anchorage, AK | Active |
| Mulberry Coop. Tel. Co. Inc. | Mulberry Cooperative Tel. Co., Inc. | Mulberry, IN | Active |