The invention relates to a data processing device, comprising a client part (120), at least one telecommunications coupler for exchanging data with an external data processing system (110), and a control device. Said client part (120) is provided with a function module coupling device for at least one mobile function module (140), said function module coupling device enabling data to be exchanged between the function module (140) and the client part (120). The control device particularly controls the exchange of data with the external data processing system according to control data that are read in from a function module (140) via the function module coupling device when a function module (140) is connected by the function module coupling device. The invention also relates to a data processing device comprising a control device, a non-volatile first memory for storing at least one file, a function module coupling device for at least one function module and a display device. Said function module has a non-volatile second memory in which a data element representing a positive credit value is stored. The control device represents the data of the at least one file stored in the first memory by means of a display device and reduces the credit value stored in the second memory according to the period of time for which the data are represented or according to the volume of data used, until the credit value is less than or equal to zero. |