If you know a person's name and address, you can use the white pages to look up his telephone number. You can use a reverse lookup directory to identify the name and address for a phone number. It so happens that there is also a way to look up a telephone service provider, if all you have is the phone number.
Visit Telecodata.us, a website that provides centralised information on telephone numbers, exchanges and companies (see References).
Click "Area/Exchange" under the Common Lookup heading.
Type the area code and the exchange (first three digits) of the phone number in the search fields and click "Search."
Review the search results. If only a single company is listed for the area code and exchange you entered, that company services all numbers for that exchange. The search results will indicate which set of phone numbers belongs to each company if multiple companies are listed. For example, in area code 718, phone numbers that begin with 208-0 are serviced by AT&T Wireless, while numbers that begin with 208-3 belong to Verizon Wireless.