E.164

The International Telecommunication Union recommendation that defines the international public telecommunication numbering plan used in the Public switched telephone network (PSTN) and some other data networks. It also defines the format of telephone numbers. E.164 numbers have a maximum of fifteen digits. A + prefix to the dialled E.164 number indicates that the E.164 number is international. The appropriate international call prefix code must be used in the E.164 number.