Abstract: To enable testing of lightly loaded, remote base stations 2, a mobile phone 3 located within the cell is programmed to dial a test number via the public switched telephone network (PSTN). The test number generates an audio signal, e.g. a fixed tone which is transmitted to the mobile phone. A test unit 4 is connected to the mobile phone and initiates the test program and monitors receipt of the audio signal. Test unit 4 includes control logic 5 connected via a communication link 54 to a base station 2, and via lines 51, 52, 53 to phone 3. A tone monitor 7 tells control logic 5 whether a radio downlink test tone has been received, and the result is stored in a memory 11. A second tone generator 8 can be actuated by control logic 5 to test a radio uplink from phone 3 to base station 2.