The Area Codes of United Kingdom:
| City/Town or Region | Area code | |
|---|---|---|
| 1. | Oakham | 01572 (+441572) |
| 2. | Oban | 01631 (+441631) |
| 3. | Okehampton | 01837 (+441837) |
| 4. | Oldmeldrum | 01651 (+441651) |
| 5. | Omagh (Northern Ireland) | 02882 (+442882) |
| 6. | Orkney | 01856 (+441856) |
| 7. | Orpington | 01689 (+441689) |
| 8. | Oswestry | 01691 (+441691) |
| 9. | Oxford | 01865 (+441865) |