An operating unit for a mobile radio telephone comprising: a housing separate from a mobile radio telephone unit which may be in data communication with the mobile radio telephone; a first set of standardized functions for mobile radio telephones which includes the functions for setting up a fixed data link and for transmitting an identity attribute of the mobile radio telephone stored in a memory module of the housing; and a library containing a second set of specialized functions for the mobile radio telephone which can be stored in the memory module of the housing.