By providing a pseudo-cell inside an aircraft, a digital mobile phone would recognise the presence of a strong local signal and would, as a consequence, turn down its RF power to a minimum thus reducing the chance of RF interference with poorly protected aircraft electronic systems. The 'aircraft cell' could be set to allow phones to be used on the ground, but block them prior to engine start. That would require the airtime service providers to enable 'roaming' on an 'aircraft cell'; such cells should have a sufficiently high calling tarriff to dissuade on-aircraft usage. But although this might be suitable for GSM, the chaotic 'Tower of Babel' system in the USA with its multiplicity of systems and operating modes would be more difficult to cater for.