What is a good source for data for look up of which carrier a phone
number belong to..... I don't care about first name, last name etc
about the phone number. I just need the cell phone carrier info. Any
one knows of good services for this purpose? Thanks in advance.

Fone Finder (www.fonefinder.net) used to provide this information, but
it appears to be down (you can see a cached version at
://www.google.com/search?hl=en&q=fonefinder.net).

The problem today is that with number portability, the carrier data
can be inaccurate. For example, I recently switched from T-Mobile to
Cingular and kept my T-Mobile prefix.