Definition
E.164 is the ITU-T international numbering plan. An E.164 number is written with a leading + followed by the country code and national number, up to 15 digits in total, with no spaces or punctuation.
An international number consists of a country code (1–3 digits) followed by the national significant number, which mobile networks split into a national destination code and a subscriber number (3GPP TS 23.003).
Messaging APIs expect numbers in E.164 so they can be routed unambiguously. Drop the national trunk prefix (the leading 0) when converting: 050 123 4567 in the UAE becomes +971501234567.
Store numbers in E.164 in your CRM. Local formats, duplicated country codes and spaces are a frequent cause of failed sends and duplicate contacts.
Some APIs and SMPP fields want the number without the +; in SMPP, set the TON to international (1) and NPI to ISDN/E.164 (1) instead.
Example
+971501234567 (UAE mobile), +966512345678 (Saudi mobile), +442071234567 (UK landline)