Definition · General
E.164
Also known as: E.164, E164, international phone number format
E.164 is the ITU-T standard that defines the international public telephone numbering plan. It specifies how phone numbers are structured globally — a leading plus sign, country code, and national number, up to 15 digits — so a number is unambiguous worldwide. APIs and telephony platforms require numbers in E.164 format.
E.164 is the format that makes a phone number portable across systems and borders: "+" followed by the country code and the national subscriber number, with a maximum of 15 digits and no spaces or punctuation. "+14155550123" is E.164; "(415) 555-0123" is the same number formatted for humans.
For front-office software, E.164 is the lingua franca under the hood. Texting and voice APIs, CRMs, and call-tracking platforms store and exchange numbers in E.164 so there is no ambiguity about country or formatting. When a CSV import fails or a number won't validate, a mismatch with E.164 is a common cause. It is a technical standard, not a pricing feature — but it is exactly the kind of term an integration or migration question turns on.
For a buyer, E.164 rarely appears on a pricing page, but it surfaces the moment you import contacts, connect an API, or move numbers between systems — knowing the format is what keeps a migration from silently dropping records.