Why are rate centers important?

In this article:

If your preferred carrier says your number is not eligible for transfer, the most likely cause is a rate center limitation on your carrier's end.

A rate center is a geographically specific area used to determine the boundaries for local calling, billing, and assigning phone numbers. Typically a call within a rate center is local, while a call from one rate center to another is a long-distance call. Rate center boundaries do not necessarily align with the county or municipal boundaries.

The rate center is determined by the area code (NPA) and prefix (NXX) of a phone number. 

If you find out that you are unable to port your number to a particular carrier, it's likely that the carrier cannot support that specific rate center. Always check with your new provider first to ensure they can support the rate center and thus your phone number. You will find more helpful resources in the following article:

Can I port a number to any wireless provider?

Additional Notes:

• All US and Canadian carriers can only support numbers that are in their country of service.
• Toll-free numbers are not supported by wireless carriers but you can port to many landline and VoIP providers to use that number.