The International Telecommunication Union (ITU) defines E.164 as a globally recognized standard for assigning telephone numbers across public switched telephone networks (PSTN) and various data networks.

The E.164 protocol provides a uniform and unique global number to each device on the PSTN that ensures calls and text messages are correctly routed to individual phones across various countries. By validating and verifying phone numbers, this formatting helps prevent fraudulent activities and ensures effective communication.

With a maximum of 15 digits, E.164 numbers integrate all the necessary information to route calls and texts through international and national phone networks, formatted as [+] [country code] [subscriber number, including area code].