Abstract: During connection set up between a mobile telephone and a base station, program data is acquired from the network for controlling its mode of operation. The mobile telephone and base station each have a memory for storing program data relating to one or more modes of operation. The base station transmits a signal indicative of a preferred mode of operation and the mobile responds with a signal indicative of whether its memory already contains program data for this mode of operation. If not, then the base station transmits the required program data. The base station and mobile telephone then operate in this preferred mode. If the mobile is not so capable (for example because it has insufficient memory), the process is repeated with different mode control programs until the most appropriate mutually compatible program is identified.