- product:numbers E.164 is the international telephone numbering plan used for public switched telephone networks (PSTN). It defines the format of phone numbers that ensures consistency across different telecommunications systems worldwide while ensuring that each number is unique. E.164 numbers are typically composed of a country code, a national destination code (NDC), and a subscriber number. The maximum length of an E.164 number is 15 digits. It excludes spaces, dashes, and parentheses, and usually begins with a plus sign (+) to indicate that it is a full international number. When dialing a number on the SignalWire platform, it is **required** to use the E.164 format. This ensures that the call is routed correctly to the intended destination. ## E.164 Number Structure: - **+ (Prefix):** Indicates an international number. - **Country Code (CC):** 1-3 digits assigned to each country (e.g., +1 for the U.S., +44 for the U.K.). - **National Destination Code (NDC):** Area or region code for a specific part of the country. - **Subscriber Number (SN):** The individual’s or businesss unique phone number. ## Example Table: | **Scenario** | **E.164 Format** | **Description** | |||-| | U.S. Mobile Number | +12125551234 | A standard mobile number in the U.S. (country code +1) | | U.K. Landline | +442071838750 | A landline number in London, U.K. (country code +44) | | India Mobile Number | +919876543210 | A mobile number in India (country code +91) | | Brazil Mobile (Sao Paulo) | +5511998765432 | A Sao Paulo mobile number in Brazil (country code +55) | | Australia Business Line | +61298765432 | A business phone in Sydney, Australia (country code +61) | | Germany Landline | +492219876543 | A landline number in Cologne, Germany (country code +49) | ## Regex Pattern for E.164 Numbers: If your application does not store numbers in E.164 format, you can use a regular expression to format them for your SignalWire application. Adhering to the [official ITU E.164 recommendation](https://www.itu.int/rec/T-REC-E.164/en) the format must be a number that starts with a plus sign (+) and has a maximum length of 15 digits. Since no [country code](https://en.wikipedia.org/wiki/List_of_country_calling_codes) starts with a 0, the first digit after the plus sign must be a number between 1 and 9. regex ^\+[1-9]\d{1,14}$ To ensure the formatted number is a valid number, you can use the [SignalWire Phone Number Lookup API](/rest/signalwire-rest/endpoints/space/lookup-phone-number) to verify the numbers validity and retrieve additional information about it.