E.123

E.123 is an international standard by the standardization 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 ITU, in E.123: "+" is the "International Prefix Symbol" used in a "Telephone number, E.123 international notation".