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.
In 2001, a legal case Telstra Corporation Ltd v Desktop Marketing Systems Pty Ltd was heard in the Australian Federal Court.
[4] In United States, landline phone subscribers can pay a small fee to exclude their number from the directory, depending on the service provider.
At the time of their campaign; they cited both privacy, and control of out of pocket costs, as reasons for their opposition.
[5] Several information companies provide reverse cell phone lookups that are obtained from various resources, and are available online.
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.