Abstract: A cellular telephone network with the capability to detect faulty cellular telephones in use in the network. The network includes measurement units at some or all of the cell sites. The measurement units monitor the radio links between each cell site and specific cellular telephones. Measurements taken at all the cell sites are accumulated at a test system controller. The test system controller stores and processes the measurements to detect faulty cellular telephones. When a faulty cellular telephone is detected, a trouble manager notifies the subscriber of the fault so that it might be repaired before the fault affects cellular telephone service. The same measurement techniques are also used to detect fraudulent telephone usage and network problems.