A mobile telecommunication station which is connected to a mobile telecommunication network and is provided with a mobile telecommunication service from the network, providing a function enabling unit (for example a voice coding unit) with a function which is masked in advance and is enabled by release of the mask and a masking control unit for watching predetermined air interface information (for example a broadcast information) from the mobile telecommunication network and releasing the mask of the function enabling unit according to an instruction, in extended information elements thereof, for releasing the mask. A half rate mobile telecommunication unit capable of increasing for example a channel capacity can therefore be released on the market early without waiting for the completion of the entire system on the network side. When the network side system is completed, the potential half rate functions of the mobile telecommunication unit are revealed all at once. The large number of already sold half rate mobile telecommunication units of high frequency utilization efficiency consequently improve the efficiency of channel utilization greatly.