1. An assistance device for a motor vehicle, the device comprising firstly a terminal ( 1 ) on board a vehicle and manual control means placed inside the vehicle and connected to said terminal, and secondly a remote processing center ( 8 ) suitable for communicating with the on-board terminal via a radiotelephone network ( 6 ), said center being suitable for handling exchanges with said on-board terminal by means of a given protocol and including, in particular for this purpose, means ( 7 ) for recognizing requests formulated verbally by the user ( 5 ) and/or requests corresponding to the user actuating manual control means, and also means for sending information to the on-board mobile terminal, the device being characterized in that the manual control means comprise a control element ( 2 ) which makes only a single type of actuation available to the user, the exchange protocol handled by the processing center ( 8 ) enabling the user to dialog with said processing center only by actuating the control element ( 2 ) and/or by formulating requests verbally.