E.164 number formatting for VoIP and phone systems

E.164 is the international numbering format used to represent telephone numbers with a country code and national significant number. In software, the canonical form normally starts with + and contains digits only after it.

Normalisation rules

• Store one canonical value, such as +61255550123.
• Keep display formatting separate from routing data.
• Remove domestic trunk prefixes when adding a country code.
• Do not infer a country from an ambiguous local number without context.
• Preserve extensions in a separate field or explicit dialling rule.
• Validate length and country-specific rules without claiming that syntax proves reachability.

E.164 assignments are maintained by the ITU. Related: international dialing codes and number portability.