Reverse phone lookup sites — like WhitePages.com, AnyWho.com and Addresses.com — are plentiful and free for landline phone numbers. But reverse phone lookup doesn’t come free for cell phone numbers. Reverse phone directories are also regularly used by law enforcement agencies and other emergency agencies. These systems are able to access both public and private phone numbers. Reverse Phone Detective Lookup contains a database of hundreds of millions of cell and unlisted phone numbers, complete with information about the owner. The phone numbers and information about each owner is collected from public information, data brokers, and other confidential sources.