Phone numbers in Old Greenwich, Connecticut
Old Greenwich has 13 phone prefixes in area codes 203, 475.
Biggest holders: MCImetro (Verizon Business), AT&T (local phone), Onvoy. This is the local calling area (rate center) where those prefixes were first assigned.
- Local phone company 23%
- Internet / business phone carrier 77%
Every prefix in Old Greenwich
Search the first six digits of a number in this list. If it's here, the number started in Old Greenwich with the carrier shown. If it isn't, check the Connecticut page or look the number up.
| Prefix | Carrier | Type | Assigned |
|---|---|---|---|
| 203-277 | MCImetro (Verizon Business) | Internet / business phone carrier | 2003 |
| 203-344 | Cablevision Lightpath | Internet / business phone carrier | – |
| 203-369 | MCImetro (Verizon Business) | Internet / business phone carrier | 2003 |
| 203-409 | Teleport Communications America | Internet / business phone carrier | – |
| 203-637 | AT&T (local phone) | Local phone company | – |
| 203-698 | AT&T (local phone) | Local phone company | – |
| 203-827 | MCImetro (Verizon Business) | Internet / business phone carrier | 2004 |
| 203-986 | MCImetro (Verizon Business) | Internet / business phone carrier | 2004 |
| 203-990 | MCImetro (Verizon Business) | Internet / business phone carrier | 2005 |
| 475-249 | AT&T (local phone) | Local phone company | 2014 |
| 475-340 | Onvoy | Internet / business phone carrier | 2023 |
| 475-465 | Onvoy | Internet / business phone carrier | – |
| 475-946 | Fractel | Internet / business phone carrier | 2020 |
Most prefixes are pooled: the 10,000 numbers in each are handed out in blocks of 1,000 to different carriers, and people can also take their numbers to another carrier. So the carrier shown is where the prefix started, not a guarantee about any one number. Source: NANPA central office code records, 2026-10-10.