1. A GPS navigation device, comprising: a touch-sensitive display configured to display map information and navigation route instructions, if the navigation device is in a normal navigation mode; a two-way wireless transceiver configured to connect the navigation device to a mobile telephone; a processor configured to, enable a user to control one or more functions of the mobile telephone through a graphical interface presented on the touch-sensitive display of the navigation device in place of map information and navigation instructions, and cause one or more control signals to be sent to the mobile telephone via the two-way transceiver, if the touch-sensitive display is displaying said graphical interface, and if the user touches said graphical interface, the control signals being configured to control said one or more functions of said mobile telephone; an audio output configured to broadcast signals received from the mobile telephone via the two-way transceiver; and a microphone configured to return data representing a voice to the mobile telephone via the two-way transceiver.