how do you find out what telephone company is providing service for a specific telephone number?

Answer 1

Use this link for starters:

http://www.telcodata.us/telcodata/telco

The only problem is that nowadays people are 'porting' their telephone numbers, meaning that if I move from one area to another, or if I switch phone companies, I can take my phone number with me. The local telco is required to move that number over to the other provider's database. So, though this link will MOST LIKELY answer your question, it's not absolutely certain.

Polly

Answer 2

NANPA
They are the ones who designate the current and future number planning in North America. Their website shows you the company provideing service, location of area codes and prefixes, and future expansion.