In the air, mobile phones will automatically go to their highest transmission power setting in order to find a ground station to log on to. This level of power is sufficient to affect aircraft systems especially if any shielding of wires has deteriated during the years of aircraft service. The system to allow mobile phone use onboard, that has been trialled on a QF B767, commands all the mobile phones onboard to their lowest power setting which has been determined to be low enough as to not affect any aircraft systems.