Twilio strongly encourages using E.164 phone number formatting for all phone numbers both in the ‘To’ and ‘From’ fields. This is an internationally-recognized standard phone number format that will help to ensure deliverability of calls and SMS messages across the globe.
This means that instead of using an International Call Prefix like 011, Twilio users should be incorporating E.164 formatted phone numbers in their API requests and TwiML scripts.
Notice: Short Code messaging numbers do not require a plus sign or country code. For more information, please see Formatting Short Code Numbers.
E.164 Phone Number Formatting
E.164 formatting for phone numbers entails the following:
- A + (plus) sign
- International Country Calling code
- Local Area code
- Local Phone number
For example, here’s a US-based number in standard local formatting: (415) 555-2671
Here’s the same phone number in E.164 formatting: +14155552671
Dialing Mobile Phone Numbers
In a number of countries internationally, local dialing may require the addition of a '0' in front of the subscriber number. With E.164 formatting, this '0' must usually be removed.
For example, here’s a UK-based number in standard local formatting: 020 7183 8750
Here’s the same phone number in E.164 formatting: +442071838750
Notice: When calling a mobile phone from Mexico, E.164 formatting requires a '1' be added after the country code.
For example, a local wireless number in Mexico City 55 1234 1234 would become +52 1 55 1234 1234 when using E.164 formatting. This call will not be completed successfully if missing the added '1'.
Help with E.164 Formatting
If you are unsure of the correct country code for a number, a good reference is this Wikipedia page that lists countries and their calling codes.
If you need additional help determining the correct E.164 formatting for a phone number, consider using Twilio Lookup. The Lookup API can help validate any phone number to make sure it is correctly formatted to send or receive calls. Lookup also offers additional options for Caller ID and Provider lookup. Learn more about the Lookup API here.