Abstract: A mobile telephone is provided that comprises: a core functional module, which includes one or more of a group of functional components necessary for operation as a mobile telephone, the group including logic circuitry, radio transmitting and receiving circuitry and audio transmitting and receiving circuitry, and a casing module which can be combined with the core functional module, wherein circuitry is associated with the casing module and wherein when the core functional module is combined with the casing module, the circuitry of the core functional module will be connected to circuitry associated with the casing module. The mobile telephone is characterised in that the appearance of the mobile phone is dictated by the appearance of the casing module, and the functionality of the mobile phone is dictated by the circuitry of the core module and the circuitry associated with the casing module.