E.164 (International Phone Number Format)
E.164 is the ITU-T international numbering plan — the +country-code format (max 15 digits) behind tel: links, SMS routing, and every CRM that wants its phone fields to actually work.
The format
An E.164 number is + followed by a 1–3 digit country code and the national significant number, maximum 15 digits total: +431234567890. It deliberately drops everything else — no trunk prefixes (the domestic 0), no spaces or punctuation, no extension (extensions are a separate convention). RFC 3966 wraps it in a tel: URI for clickable dialing.
National formats diverge wildly — trunk prefixes, mobile vs landline patterns, variable lengths — which is why formatting is non-trivial: you need per-country numbering-plan data (the libphonenumber approach) rather than regexes.
Why CRMs insist on it
Mixed-format phone fields break dedup, click-to-call, and SMS campaigns. Normalizing to E.164 at import — which our formatter does in bulk for 240+ countries — makes phone a usable key instead of a text field, and it is what vCard and API payloads expect.
Related Standards
- •ITU-T E.164 — international public telecommunication numbering plan
- •RFC 3966 — tel: URIs
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