You can find businesses, organizations, and the phone numbers and addresses of people by name or reverse lookup based on a telephone number using online search sites. Some excellent sites are:

Infospace.com

Provides yellow and white page lookups as well as reverse lookups, maps and directions, and email search.

Yellow.com

Provides yellow pages services from multiple sources.

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Find people through their phone number, address, or other means; includes a variety of Web-based methods such as address and phone lookups.