Reverse telephone directory

A reverse telephone directory (also known as a gray pages directory, criss-cross directory or reverse phone lookup) is a collection of telephone numbers and associated customer details. However, unlike a standard telephone directory, where the user uses customer's details (such as name and address) in order to retrieve the telephone number of that person or business, a reverse telephone directory allows users to search by a telephone service number in order to retrieve the customer details for that service.

Reverse telephone directories are used by law enforcement and other emergency services in order to determine the origin of any request for assistance, however these systems include both publicly accessible (listed) and private (unlisted) services. As such, these directories are restricted to internal use only. Some forms of city directories provide this form of lookup for listed services by phone number, along with address cross-referencing.

Publicly accessible reverse telephone directories may be provided as part of the standard directory services from the telecommunications carrier in some countries. In other countries these directories are often created by phone phreakers by collecting the information available via the publicly accessible directories and then providing a search function which allows users to search by the telephone service details.

Printed reverse phone directories have been produced by the telephone companies (in the United States) for decades, and were distributed to the phone companies, law enforcement, and public libraries. In the early 1990s, businesses started offering reverse telephone lookups for fees, and by the early 2000s advertising-based reverse directories were available online, prompting occasional alarms about privacy concerns.

In 2001, a legal case Telstra Corporation Ltd v Desktop Marketing Systems Pty Ltd was heard in the Australian Federal Court. gave Telstra, the predominant carrier within Australia and the maintainer of the publicly accessible White Pages (residential) and Yellow Pages (commercial) directories, copyright over the content of these directories.

In February 2010 a Federal Court of Australia case Telstra Corporation Ltd v Phone Directories Company Pty Ltd determined that Telstra does not hold copyright in the White Pages or the Yellow Pages.

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