E.164 is the international telephone numbering plan that ensures each device on the PSTN has globally unique number.
This number allows phone calls and text messages can be correctly routed to individual phones in different countries.
According to the official ITU E.164 recommendation, the format must be a [+] [country code] [subscriber number including area code] and can have a maximum of fifteen digits.
Examples of E.164 Numbers
| E.164 Format | Country Code | Country | Subscriber Number |
| +14155552671 | 1 | US | 4155552671 |
| +442071838750 | 44 | GB | 2071838750 |
| +551155256325 | 55 | BR | 1155256325 |
