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NPA-NXX-Xs (Thousand blocks)

Telephone numbers are typically assigned to carriers in chunks of 1000 numbers. These chunks are called NPA-NXX-Xs, "thousand blocks" or simply "blocks". These blocks are the minimum unit of TNs that can be assigned to a carrier.

Remember that Local Number Portability (LNP) allows users to move their numbers between carriers. Each NPA-NXX-X has an assignee (original carrier of record), but you can not assume that every TN encompassed in an NPA-NXX-X is serviced by that carrier.

To determine the current carrier for a particular TN, use the [Telephone Number Info API] (/api/docs/api/telephone-number-info), but you'll need to qualify in order to gain access to that data.

NPA-NXX-X blocks have one of these statuses, as defined by NANPA:

  • AS: The block has been assigned to a service provider (active)
  • RT: The block is being "retained" by the service provider (not active)
  • AV: The block is available for assignment (not active)
  • AP: The block is pending assignment to a service provider (pending)
  • AF: The block has a future effective date (pending)

Common uses of this API are to find the carrier assignee for an NPA-NXX-X block:

GET /api/npaNxxXs/8583807

To conduct analysis on number utilization:

GET /api/npaNxxXs/?rateCenter=POWAY&state=CA
GET /api/npaNxxXs/?npa=207&status=RT

While we make every effort to keep this data accurate and up-to-date, your mileage may vary. Please contact api-support@numberbarn.com with any comments, concerns, or corrections.