Teleprinting system, at a telephone user comprising an apparatus formed by a microprocessing unit (12) connected to a telephone line (16) through a modulating-demodulating or modem system (14). Data transmis­sion messages are distinguished from standard telephone messages for example by means of differences in the ring signal. The received data are sent to a printer, (22) to a display (38) or, through an interface circuit (30) to an outer computer, and by which messages are received from an op­tical reader (34) or from a keyboard (42) for their transmission through the modem unit (14) to the corresponding apparatus of an agency or indi­vidual connected in order to embody said interaction. Said teleprinting system is particularly suitable to embody telebilling or teleinvoicing methods from service agencies to an end user.