You can check out phone numbers and addresses on sites like people.yahoo.com and anywho.com. If you want to verify the general area of a phone number that isn't listed check out fonefinder.net.
If you think the address given to you might be a mail drop (which are commonly used by scam artists) you can check that out as well here: www.finaid.com/scholarships/maildropsearch.phtml
Many counties throughout the United States also list property records online. You can easily find out the owner of the address given to you at www.skipease.com/property.html. If there is no online database, you can call the tax assessor for the county to find out who owns the property. It's all public information.
A number of online searches to find out more information on individuals is available at black book online.
Always make sure the info they give you checks out before you proceed with a transaction.
(Great info provided by LayitLow.com)