reverse phone directory(also known asgrey pagesTable of contents,criss-cross directoryorReverse phone lookup) is a collection of phone numbers and related customer details. However, unlike a standard phone book, where a user uses a customer's details (such as name and address) to retrieve that person or business's phone number, a reverse phone book allows users to search by phone service number in order to Retrieve customer details for the service.
Law enforcement and other emergency services use reverse phone books to determine the source of any request for assistance, but these systems include both public access (listed) and private (not listed) services. Therefore, these directories are limited to internal use only. Some forms of city directories provide this form of lookup of listed services through telephone numbers and address cross-references.
In some countries, telecom operators may offer a publicly accessible reverse phone book as part of the standard directory service. In other countries, these directories are often created by phone stealers by collecting information available in publicly accessible directories and then providing a search function that allows users to search by phone service details.