morning folks,
voip providers use certain ranges of phone numbers, does anybody know how to find a provider by a given phone number?

You can't really be sure without a dip into the LERG. You can use http://www.localcallingguide.com/ to get an idea, but just because the entire NPA-NXX or a 1000's block says it's Pac Bell, it doesn't mean that the specific number hasn't been ported and is still with Pac Bell.