Improved modular telecommunications device

A communication device is disclosed which includes a wireless communicator part for use with a cellular telecommunications network and a supplementary part to which the wireless communicator part is coupleable. The wireless communicator part has an associated identifier for uniquely identifying it to the network. The supplementary part also has an associated identifier for uniquely identifying it to the network. The identifiers enable the network to determine the functional attributes of the part with which the identifier is associated. Embodiments are described which allow the network to always be aware of the functional attributes of the device. The functional attributes of the device will change depending upon the coupling and uncoupling of the wireless communicator part to the supplementary part. The identifiers may be IMEIs and may be transmitted as a USSD string.