The invention provides a portable and autonomous assistance device to derive information on faults in a private telecommunication installation comprising particularly equipment units to assist the client owning the installation in maintaining the latter. A maintenance session is selected in a maintenance server of the service provider managing the installation as a function of information transmitted by the assistance device so as to provide instructions in the device. The address of the server and an identifier of the equipment unit are rapidly read by means of a bar code reader which can also read bar codes in a user manual. The assistance device also serves to configure a terminal (TE) by means of a configuration session opened in a server (SFT) of the terminal manufacturer.