The invention provides an electronic mobile communications/entertainment device capable of a plurality of modes of operation, comprising a basic module having circuitry common to the operation of the device in said plurality of modes of operation, and a plurality of supplementary modules, each supplementary module being provided in the form of a housing cover for the device and including controlling means configured to provide for a corresponding mode of operation when coupled to the basic module, the supplementary modules being interchangeably attachable/detachable to the basic module so as to provide respective modes of operation, and the device only being operational when one of said plurality of supplementary modules is attached to the device.