The invention relates to an internal communication terminal (iK1, iK2, iK3) of a private branch exchange (PBX), having at least one device (E11, . . . , E32), by means of the activation (act) of which said internal communication terminal (iK) or the private branch exchange (PBX) is put into a state in which said internal communication terminal or the private branch exchange identifies the telephone number of an incoming call from an external communication terminal (eK). The identified telephone number of the external communication terminal is then associated with the internal communication terminal in a database (DB), provided that the type of the association of said external communication terminal with said internal communication terminal connected with the activation of said device is not yet entered in the database. Otherwise, said association is deleted.