E.123

E.123 is an international standard by the Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T), entitled Notation for national and international telephone numbers, e-mail addresses and Web addresses.^[1] It provides guidelines for the presentation of telephone numbers, email addresses, and web addresses in print, on letterheads, and similar purposes.

As described by the standard, ⟨+⟩ is the international prefix symbol, should precede the country code, and serves to identify the number following as the international telephone number.