United States Phone Numbers: Format, Area Code & Validation Guide - phone-number-standards -

Frequently Asked Questions

The North American Numbering Plan (NANP) format is +1 NXX NXX XXXX, where +1 is the country code, NXX is the three-digit area code, followed by the three-digit central office code and the four-digit subscriber number. This standardized format simplifies communication across North America and the Caribbean.
Use a regular expression like `/^+1([2-9]\d{2}[2-9]\d{2}\d{4})$/` to validate 10-digit US phone numbers, including the +1 country code. For more robust validation, incorporate a lookup against a current list of valid area codes and consider edge cases like spaces and hyphens.
Pennsylvania requires 10-digit dialing due to the increasing use of overlay codes, which assign multiple area codes to the same geographic region. This change accommodates the growing number of phone lines and new area codes, ensuring calls are routed correctly.
Pennsylvania uses multiple area codes across five regions, including 814 and 582 in the Northwest, 570 and 272 in the Northeast, a complex overlay system in the Southeast, 717 and 223 in the Central region, and 412, 724, and 878 in the Western region. 10-digit dialing is required statewide.
E911 compliance ensures that location information is provided to 911 dispatchers during emergencies. The FCC mandates compliance, requiring accurate location identification and transmission, especially for VoIP and location-dependent services. This includes providing dispatchable location data like street address and room number.
Number portability allows users to keep their numbers when switching providers. Developers should account for this by considering that a number previously associated with a landline might now be mobile, which can affect SMS handling and other services.
Area codes are essential for routing calls to the correct geographic location. They are three-digit codes that identify specific regions within the North American Numbering Plan. The North American Numbering Plan Administrator (NANPA) manages and assigns these codes.
Update your phone number validation rules regularly as new area codes are implemented and regulations change. Subscribe to NANPA notifications to stay informed about these updates and maintain accurate validation in your applications.
The North American Numbering Plan Administrator (NANPA) manages and assigns area codes within the North American Numbering Plan (NANP). Staying updated on NANPA's latest area code assignments is crucial for maintaining accurate phone number validation and application functionality.
While regex can check format and length, it's insufficient for thorough validation. You should also verify area codes against a current list from NANPA, handle input variations like spaces and hyphens, and account for international numbers if applicable.
Number portability, allowing users to keep their number when switching providers, impacts developers as a number's service type (landline or mobile) can change. This necessitates adapting SMS and other service functionalities accordingly.
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