Number portability
The ability to keep a phone number when switching from one carrier to another.
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The ability to keep a phone number when switching from one carrier to another.
Number portability is the regulatory requirement that lets a subscriber move their phone number to a different carrier without changing the number itself. In the US it has applied to wireline numbers since 1997 and to mobile numbers since 2003.
For anyone validating phone data, portability is the single biggest reason you cannot infer a carrier from the number itself. The NPA-NXX prefix tells you which carrier the block was originally assigned to, not who serves the number today. A number issued by one carrier a decade ago may now sit with a completely different network, or on a VOIP platform.
The only reliable way to know the current carrier and line type is a live database lookup that reflects porting activity. This is why a static area-code table cannot answer "is this number mobile?" and why PhoneCheckr queries current carrier data for every number rather than parsing the digits.
Related terms
- NPA-NXX — The first six digits of a North American number: the area code plus the three-digit exchange prefix.
- Carrier lookup — Querying network data to find which carrier currently serves a phone number.
- Line type — The classification of a phone number as mobile, landline, VOIP, or invalid.