Two long-term goals of our research is to develop a standardized communication interface between the mobile device and other onboard systems and to create a parametrical, scaleable user interface, both with voice and graphical user input/output. This paper describes the main requirements, principles and aspects of a voice/graphical user interface and of a Bluetooth based communication interface. Requirements and limitations for the implementation of speech synthesis on mobile devices will also be introduced. As a sample application of a mobile device on a vehicle an SMS-reader application will be presented.