Tracing telephone number prefixes
I recently had a project where I needed to find out what telco served users based on their phone number (US only). Area code tables are a dime a dozen, but only give you the state, and I needed finer granularity than that, including the ability to drill down to the first three digits of the local phone number, for a total of 6 digits known in industry parlance as the NPA-NXX.
The solution I found is to go straight to the source: the website of the company tht administers the North American numbering plan on behalf of the FCC (the NANP actually covers more than the US, including Canada and some Caribbean countries, but the registrar I am refering to only covers the US).
They have a very convenient page with downloadable tables of NPA-NXX to carrier assignments. As an example, here is the entry for my home phone number:
| State | NPA-NXX | OCN | Company name | Rate center | Switch | Use |
|---|---|---|---|---|---|---|
| CA | 415-359 | 9740 | Pacific Bell | SFNC CNTRL | SNFCCA12DS0 | Assigned |
OCN is the operating company number, a numeric code they use for carriers. The “rate center” (usually the city or town name) is unfortunately encoded using the proprietary Telcordia Common Language standards rather than in plain English, and you need to pay a license fee to get that database. The carrier name also varies wildly. Pac Bell has been fully subsumed under the SBC brand name, but the old identity still linger in these tables (Verizon, in contrast, has been much more diligent at having these tables updated, even when the pre-merger name is still mentioned).
With number portability, specially the forthcoming wired to wireless number portability required by the FCC, this information will be less useful as you will be able to have, say a New York phone number but actually be in Tokyo using a Vonage VoIP box (possibly even one with a ported number), but it is still a useful resource that is not widely known.
Update (2004-10-25):
This page is the most popular Google search on my website. If all you want is to look up a phone number and don’t want to go through the hassle of importing all the NANPA tables, there are a number of NPA-NXX search pages available on the web.