How to look up which carrier holds a prefix
What's public
NANPA publishes central-office code assignments: for every active NPA-NXX, the holder's company name, its Operating Company Number (OCN), the rate center, and whether the prefix participates in thousands-block pooling. This site's prefix tables are built directly from those files, refreshed with each data update.
The lookup
Find the area code, open its prefix table, and filter by the three-digit prefix. The carrier column shows the code holder of record. For pooled prefixes, remember individual thousands-blocks may be allocated to other carriers.
The porting caveat
Code-holder data describes blocks, not individual numbers. Any single number may have been ported to a different carrier while keeping its prefix. Real-time per-number carrier lookups run against private routing databases and are not public data.
Reading the result
Two details trip people up: the company name is the legal entity, which often differs from the consumer brand (Cellco Partnership is Verizon Wireless), and an old assign date does not mean the block is dormant — blocks stay with carriers through decades of rebranding and mergers.
Sources
FAQ
Can I find which carrier serves a specific full number?
Not from public data. Block-level holder information is public; per-number routing after porting is carrier-internal.