| CoID | Company | Type | Status | States Served | 24X7 Phone |
| OEY | Integra | CLEC Facility | A | MT | 877-679-9432 |
| OFFR | RateTel Inc | 9-1-1 Admin-CPE ALI (9-1-1 Jurisdiction/PSAP ONLY) VoIP Reseller VoIP Provider | A | USA - Nationwide | 832-900-8611 |
| OFLLC | Orange Fiber LLC | VoIP Provider | A | USA - Nationwide | 904-447-7700 |
| OGDEN | Ogden Telephone Company | ILEC | A | IA | 515-275-4990 |
| OGDMI | Ogden Telephone Company | ILEC | A | MI | 517-443-5595 |
| OGMC | Ogden Regional Medical Center | 9-1-1 Admin-CPE ALI (9-1-1 Jurisdiction/PSAP ONLY) | A | UT | 801-299-2468 |
| OGT | Integra Telecom of Oregon | CLEC Facility | CLEC Reseller | CLEC UNE | Internet Protocol Relay Provider | A | MN | ND | OR | WA | UT | 877-679-9432 |
| OGTCO | Integra Telecom of Colorado (Cancelled) | Facility | C | CO | 720-325-1000 |
| OGTMN | Integra Telecom of Minnesota - North (Cancelled - See OGT) | CLEC | C | MN - North | 503-748-2020 |
| OGTMP | Integra Telecom of Minnesota (Cancelled - See OGT) | ILEC | C | MN - Scott and Rice County | 877-679-9432 |
| OGTMS | Integra Telecom of Minnesota (Cancelled - See OGT) | CLEC | C | MN - Metro Area | 877-679-9432 |
| OGTUT | Integra Telecom of Utah (Cancelled - See OGT) | CLEC | C | UT | 877-679-9432 |
| OGTWA | Integra Telecom of Washington (Cancelled - See OGT) | CLEC | C | UT | 877-679-9432 |
| OH12 | Oswego Health - CANCELLED | VoIP | C | NY | 315-349-5511 |
| OHI | Optimum Health Institute - CANCELLED | PBX | C | CA | 800-829-1011 |
| OHIOU | Ohio University | PBX/PS911/Shared Tenant | A | OH | 740-593-1911 |
| OHLVD | Lima City School District (CANCELLED) | PBX | C | OH | 419-549-7540 |
| OHM | Ohio Telecom Inc | CLEC Facility | A | OH | 419-734-2369 |
| OHSD | Oak Harbor School District(Inactive) | Co-OP/Rural, PBX/PS911/Shared Tenant | C | WA | 360-672-4213 |
| OIA | CommChoice | Facility | A | IA | 712-271-2710 |
| OIIL | Owens-Brockway Glass Container - CANCELLED | PBX | C | IL | 815-673-5171 |
| OIN | Oneida Indian Nation (INACTIVE) | PBX | C | NY | 315-829-8100 |
| OIPV | One IP Voice, Inc. (CANCELLED) | VoIP Reseller | C | Continental US | 866-547-4706 |
| OIT | State Of Maine | PBX/PS911/Shared Tenant | A | ME | 207-624-8845 |
| OIT01 | Orsini IT LLC | VoIP Provider | A | USA - Nationwide | 305-967-6756 |
| OKMN | TDS Telcom Oakman (Cancelled) | TDS | C | Oakman, Flatwood, Nauvoo, Lynn, Grayson, AL | 205-622-3325 |
| OKWTC | Oklahoma Western Telephone Company | ILEC | A | OK | 405-826-4560 |
| OLCC | Orange Lake Resort & Country Club(Inactive) | ILEC | C | FL | 407-239-1141 |
| OLICO | Peninsula Fiber Network LLC | CLEC Facility | A | MI | 888-564-8881 |
| OLT | Olin Telephone Company | ILEC | A | IA | 319-981-6908 |
| OLYMP | Olympus Communications LLC - CANCELLED | CLEC Facility | C | IA | MN | 712-260-8414 |
| OMBX | AAA Enterprise Solutions Inc. O/A Ombrex Telecom | VoIP Reseller VoIP Provider | A | USA - Nationwide | 437-800-5438 |
| OMCWP | Ozarks Healthcare | PBX/PS911/Shared Tenant | A | AR | MO | 417-256-9111 |
| OMEGA | VoiceLogix LLC | PBX/PS911/Shared Tenant Video Relay Service VoIP Provider | A | USA - Nationwide | 772-559-4794 |
| OMH | Long Lines Metro | Facility | A | Eastern SD | Western IA | 605-422-1200 |
| OMNI | OmniTel Communications | CLEC | A | IA | 800-417-8685 |
| OMNIS | OmniSource (CANCELLED) | PBX/PS911/Shared Tenant | C | IN | 260-422-5541 |
| OMPT | Omnipoint Communications Services (Cancelled) | Wireless | C | USA | 206-663-7927 |
| OMS12 | Onemind Services LLC | 9-1-1 Admin-CPE ALI (9-1-1 Jurisdiction/PSAP ONLY) Internet Protocol Relay Provider VoIP Reseller VoIP Provider | A | USA - Nationwide | 408-540-6771 |
| OMTWO | OM2 Technology Inc. - CANCELLED | PBX | C | All United States | 866-662-4911 |
| OMX | Intrado Life & Safety Inc. - CANCELLED | PBX/PS911/Shared Tenant | C | 4807198557 | 4807198557 |
| ONC | onCloud MSP | VoIP Provider | A | USA - Nationwide | 470-305-1234 |
| ONDR1 | ON DRIVE TECHS | VoIP Provider | A | USA - Nationwide | 866-258-0064 |
| ONE | OneCloud Networks | VoIP Provider | A | NY | TX | 972-941-3139 |
| ONEC | One Choice Technology | PBX/PS911/Shared Tenant | A | IL | IN | 317-755-8825 |
| ONELK | OneLink Communications (CANCELLED) | Digital Cable, VoIP | C | PR | 787-620-9999 |
| ONEPO | OnePointSync | VoIP Reseller | A | USA - Nationwide | 303-586-5745 x103 |
| ONES | Onestar Long Distance, Inc. (Cancelled) | Facility | C | ME, MA | 800-482-0000 |
| ONESC | OneSource Telecom | PBX/PS911/Shared Tenant VoIP Reseller | A | TX | 512-763-4600 |
| ONG | TheIPGuys.Net LLC dba OneNet Global | PBX/PS911/Shared Tenant VoIP Reseller VoIP Provider | A | USA - Nationwide | 952-960-1010 |