| CoID | Company | Type | Status | States Served | 24X7 Phone |
| ONVOY | Onvoy Spectrum LLC | CLEC Facility VoIP Provider | A | USA - Nation Wide | 855-404-4768 |
| ONW | Connect Communications, LLC (CANCELLED) | Facility | C | North Carolina | 828-312-9702 |
| OOMA | Ooma Inc | VoIP | A | US | 888-711-6662 |
| OONE | O1 Communications Inc. | CLEC Facility | VoIP Provider | A | USA | 888-444-1111 |
| OOU | ConnectTo Communications LLC - CANCELLED | CLEC Facility | C | CA | 8665290542 |
| OPC | The Other Phone Co/Access One Comm (Cancelled) | Facility | C | LA, MA, AL, TN, KY, NC, SC, GA, FL | 800-547-7101 |
| OPNTV | OpenTV, Inc. Cancelled) | PBX | C | CA | 800-604-4005 |
| OPS9 | City of Opelika AL (dba Opelika Power Services) - CANCELLED | CLEC Facility; CLEC Reseller | C | AL | 334-705-5570 |
| OPSYS | OPSYS - CANCELLED | VoIP Reseller VoIP Provider | C | USA - Nationwide | 305-216-4945 |
| OPT | Blue Valley Technologies Inc. | CLEC Reseller | Co-Op/Rural | A | Kansas | 785-799-3311 |
| OPTC | Optical Telecommunications | Cable Digital CLEC Facility CLEC Reseller CLEC UNE VoIP Provider | A | FL | 305-779-7777 |
| OPTEL | OpTel, Inc. (Cancelled) | Facility & PBX | C | AZ, CA, CO, FL, IL, IN, TX | 800-322-1021 |
| OPTI | NP Information Systems | VoIP Provider | A | USA - Nationwide | OR | WA | WY | 253-852-1543 |
| OPTIS | OptiSolar(Cancelled) | CLEC Facility, VoIP | C | CA | 916-746-3007 |
| OPTM | OptimERA Inc. d.b.a. OptimERA Wireless | Wireless/Cellular/PCS | A | AK | 907-581-7829 |
| OPTPR | Optivon LLC | CLEC Facility CLEC Reseller VoIP Reseller VoIP Provider | A | USA - Nationwide | 787-625-8800 |
| OPTUS | Optivon, Inc. (CANCELLED) | VoIP | C | FL, CT | 813-600-6090 |
| ORANT | Oran Mutual Telephone Company | ILEC | A | IA | 563-920-2859 |
| ORBT1 | Orbital Sciences Corp - CANCELLED | CLEC | ILEC | C | USA | 800-773-7911 |
| ORCSD | Orcutt Union School District - CANCELLED | ILEC | C | CA | 805-478-4311 |
| ORCT | Town of Orange | VoIP Provider | A | CT | 203-891-2130 |
| ORG99 | OregonTel, LLC (INACTIVE) | Facility | C | OR | 503-474-7720 |
| ORL | Cordia Communications Inc (CANCELLED) | Reseller | C | FL, NY, PA, NJ | 407-766-5921 |
| ORLAN | OrLANtech Inc. | 9-1-1 Admin-CPE ALI (9-1-1 Jurisdiction/PSAP ONLY) VoIP Reseller | A | USA - Nationwide | 407-770-0493 |
| ORM | Coon Rapids Municipal Utilities | facility | A | IA | 712-999-2225 |
| ORW | Consolidated Communications of Ohio Company f/k/a The Orwell | ILEC | A | OH | 916-746-3000 |
| OSCFL | Osceola County Government | 9-1-1 Admin-CPE ALI | A | FL | 407-742-5611 |
| OSF | OSF Healthcare System - CANCELLED | 9-1-1 Admin-CPE ALI (9-1-1 Jurisdiction/PSAP ONLY) | PBX/PS911/Shared Tenant | C | USA | 309-662-3311 |
| OSM | Osage Municipal Utilities | Cable Digital CLEC Facility Wireless/Cellular/PCS VoIP Provider | A | IA | 641-832-3731 |
| OSN | OneStream Networks LLC | VoIP Provider | A | USA | 585-563-1850 |
| OSSD | Orange Southwest School District | 9-1-1 Admin-CPE ALI (9-1-1 Jurisdiction/PSAP ONLY) | A | VT | 802-249-7326 |
| OSSU | Orleans Southwest Supervisory Union | PBX/PS911/Shared Tenant | A | VT | 802-595-2733 |
| OSTEL | OneSource Teleservices (Cancelled) | Facility | C | NV | 702-210-8323 |
| OSTKO | Overstock | PBX/PS911/Shared Tenant | A | KS | PA | UT | WA | 801-947-5181 |
| OSUMC | Ohio State University Wexner Medical Center | PBX/PS911/Shared Tenant | A | OH | 614-293-8500 |
| OTC | ORLANDO TELEPHONE COMPANY DBA SUMMIT BROADBAN | CLEC Facility | A | FL | 407-996-8900 |
| OTCOR | Oregon Telephone Corporation | ILEC | A | OR | 541-932-4900 |
| OTE | Consolidated Communications of Central Illinois Company | Co-Op/Rural | A | IL | 916-746-3000 |
| OTECH | Oldham Technology - CANCELLED | VoIP Provider | C | USA - Nation Wide | 801-877-2155 |
| OTG | Omega Technology Group | VoIP Reseller VoIP Provider | A | GA | 706-776-6945 |
| OTGNY | OTG GROUP CORP | VoIP Provider | A | USA - Nationwide | 646-630-8725 |
| OTR | Otter Tail Telcom | 9-1-1 Admin-CPE ALI (9-1-1 Jurisdiction/PSAP ONLY) CLEC Facility CLEC Reseller CLEC UNE PBX/PS911/Shared Tenant VoIP Provider | A | MN | 218-998-2000 |
| OTS | Oahu Transit Services Inc | PBX | PS911/Shared Tenant | A | HI | 808-848-4400 |
| OTSCO | Otsego County 9-1-1 Communications - CANCELLED | PBX | C | Otsego Couty | 607-547-5351 |
| OTSD | Oregon Trail School District | VoIP Provider | A | OR | 503-720-8850 |
| OTT | Oklatel Communications Inc. | ILEC | A | OK | 918-656-3233 |
| OTTLN | Otterbein Lebanon Retirement Community | PBX | A | Lebanon | OH | 513-932-2020 |
| OTZ | OTZ Telephone Cooperative | Co-Op/Rural ILEC Wireless/Cellular/PCS | A | AK | 920-351-4054 |
| OUHSD | Oxnard Union High School District | PBX/PS911/Shared Tenant | A | CA | 805-512-2274 |
| OUPD | Oakland University | PBX/PS911/Shared Tenant | A | MI | 248-370-3331 |