E.123 national is the standardized numbering format for national phone numbers established by the International Telecommunication Union (ITU). It specifies the numbering plan for how phone numbers should be formatted and structured within a specific country.
E.123 national format
The E.123 national format contains the following components:
- Area code: The 1- to 3-digit area code placed within the parentheses. It identifies the geographic region within a country. Note that this is also called a “dialing code” in some regions.
- Local phone number: The unique number that identifies a specific phone line within the defined area code. It can be up to 11 digits long, depending on the country’s numbering plan. For instance, the United States and Canada use the North American Numbering Plan, where phone numbers are 7 digits long. In contrast, most European countries have a subscriber number length of 8 or 9 digits.
- Trunk prefix: This is usually a zero (0) that replaces the country code when making a domestic call.
The full E.123 national format, including the parentheses, would look like this: (123) 456-7890
E.123 national vs. E.123 international
While E.123 national uses parentheses to separate the area code and local number, E.123 international includes a plus sign (+) followed by the country code and phone number.
Unlike the plus sign in international numbers, the parentheses in E.123 national are not mandatory and can be omitted when dialing from within the same country.
E.123 national is regulated by the same standard as E.123 international, which provides the formatting guidelines for telephone numbers, email addresses, and web addresses published by the ITU.
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