The invention concerns a monitoring system for monitoring incoming telephone calls routed through a call transference system, the system comprising an electronic processor and an associated database, the system being adapted to detect the originating number of the caller and the called number to which the incoming call was made before being transferred, to automatically generate a return call to any incoming call the originating and called numbers of which have been identified without answering the incoming call, and to store the time and date of an incoming call the number of which has been identified and data representing the number to which the incoming call was made.