E164numerointijärjestelmää

E164numerointi refers to the international numbering plan for public telecommunication services, as defined by the International Telecommunication Union (ITU) in Recommendation E.164. This standard specifies the structure and format of telephone numbers to ensure they can be uniquely identified and routed globally. The key features of E.164 numbering include a maximum of 15 digits, consisting of a country code followed by a national significant number.

The country code, assigned by the ITU, identifies a specific country or geographic region. For example, +1 is for North America, +44 is for the United Kingdom, and +358 is for Finland. Following the country code is the national significant number, which is allocated by the national telecommunications authority of each country. This national number can include an area code and the subscriber's local number.

E.164 numbering facilitates seamless international telecommunications by providing a standardized framework for dialing. When making an international call, users typically dial the international access code (e.g., 00 in many countries, or + from mobile phones), followed by the country code and the national significant number, omitting any leading zeros that might be used for domestic dialing. This system ensures that calls can be routed correctly across different networks and countries. The E.164 standard is fundamental to the operation of the global public switched telephone network (PSTN) and increasingly for Voice over IP (VoIP) services.