Reverse phone lookup can be useful when trying to determine the identity or origin of an unknown number on one's caller ID or a phone bill. In addition to a person or business name, information such as address and directions are also retrieved through reverse lookup services.
Basic reverse phone lookup services are free and are offered by online directories such as Whitepages and Yellowpages. The owners of unlisted numbers and cell phones aren't provided through basic reverse phone lookup services, but many directories offer the option for a fee. Similar to reverse phone lookup, many directories offer reverse address lookup as well.