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.
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.
As it currently stands there is no legal way to ensure a particular number is not listed in the directories currently available.
United States 
|This section does not cite any references or sources. (February 2012)|
In United States, landline phone subscribers can pay a small fee to exclude their number from the directory. This service is usually called "Your Listing Not Published" and the cost ranges between $0.80 to $1.50 for residential customers. However, it is a myth that delisting is possible for cellular numbers, because each cellular carrier has a separate database.
As cellular phones become more popular, there has been debate about releasing cell phone numbers into public 411 and reverse number directories. (S. 1963, the "Wireless 411 Privacy Act" 9/2004). However, opposition led by leading consumer-protection organization Consumers Union presented several privacy concerns in their congressional testimony. Right now, cell phone numbers are not available in any public 411 or reverse-number directories. However, several information companies provide reverse cell phone lookups that are obtained from utility resources, and are available online. Because there is no central database of cell phone numbers, reverse phone directories that claim to be free cannot return information on those numbers.
In recent years community web based services offer a reverse telephone directory of known telemarketers, debt collectors, fund raisers, and other solicitors which contact consumers by telephone. Users of these services can perform a search of the telephone number which showed up on their caller ID and read through user comments to find the identity of the calling company or individual.
There are several websites available which provide results such as the owner information, address and even the providing carrier of a landline number. Many of these websites charge a fee for this service.
United Kingdom 
In the United Kingdom proper, reverse directory information is not publicly available. However, in the Channel Islands it is provided in the printed telephone directories.
Although the information is, of necessity, available to emergency services, for other agencies it is treated as 'communication data' in the RIPA regime and subject to the same controls as requests for lists of and content of calls.
- Federal Court of Australia. "Telstra Corporation Limited v Desktop Marketing Systems Pty Ltd (2001) FCA 612 (25 May 2001)". Australasian Legal Information Institute. Retrieved 2008-01-03.
- "Private parts - PLPR 25; (2001) 8 PLPR 24". Australasian Legal Information Institute. Retrieved 2008-01-03.
- Maiden, Malcolm (16 December 2010). "Copyright to enter a new dimension". The Sydney Morning Herald. Retrieved 20 December 2012.