Mobile telephony

An interface is provided between a satellite telephone system and a wireless telephone system for allowing calls to a user's wireless telephone to be diverted to a satellite telephone handset when the user is unable to use his wireless telephone, for example when on board an aircraft fitted with a satellite telephone system. The interface unit emulates the operation of a normal base station, so that the host wireless telephone system acts as if the mobile user's terminal is roaming on the host network, but is currently "busy". The user inserts a card (which may be the SIM of his mobile phone, or a card compatible with existing satellite telephone equipment) into a suitable reader in the satellite telephone, which causes the satellite ground station's card verification system to connect to a host wireless telephone network.