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. If a call attempt is initiated before this process is complete, the process is curtailed, such that the base 
station and mobile telephone identify programs already stored in the memory, but make no attempt to load a new program, as this could 
delay call set-up.