The invention discloses a mobile telephone device as part of a hands-free device in a motor vehicle. Known mobile telephone devices can be expanded only to a limited extent in their functions and functionalities by connecting peripheral devices such as for example headphone-microphone combinations. The new mobile telephone device is to be flexibly expandable by components or functionalities. For that purpose a base member (1) has a receiving means (8) for receiving a module unit (20). The module unit (20) is conductingly connected to the control device by a connecting device (21) with contact elements at the module side and contact elements at the receiving means side. The module unit (20) has analog and/or digital function units and/or analog memory units. The module unit can be for example in the form of an expansion card or memory card. By inserting a module unit (20) into the mobile telephone device it is expanded by the function which is predetermined by the respective module unit (20). By changing the module units the selection of the available functions of the mobile telephone device can be flexibly altered.