Numbering

E.164

E.164 is the ITU-T international public-telecom numbering plan. It defines the format used worldwide: a leading + followed by a country code (1-3 digits) and a national number, max 15 digits total. Every modern SIP/PSTN system uses E.164 as the canonical format.

Format

+<country-code><national-number>
+1 555 123 4567        # United States, NPA 555
+44 20 7946 0000       # United Kingdom, London (020)
+972 3 612 1234        # Israel, Tel Aviv
+81 3 1234 5678        # Japan, Tokyo

Why always normalize

E.164 is the only format guaranteed unambiguous. 020 7946 0000 means London if you're in the UK, but is meaningless from anywhere else. Always store and route on E.164. Display localized formats only at the UI layer, using a library like libphonenumber.

Country code reference

Full ITU-T E.164 country code list: ITU Operational Bulletin. DIDHub supports DIDs in 130+ country codes — see area-codes index.

Related terms