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. 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.