Abstract: A telephone exchange of the time-division-multiplex type is provided with several synchronized circulating memories whose operating cycle is divided into, say, 100 phases corresponding to respective time slots of a communication frame whereby a multiplicity of conversations can be initiated and carried on simultaneously between calling and responding subscribers. These memories include a caller memory I, a responder memory N, a monitoring memory LP, a counting memory LK, and two ancillary memories LT.sub.1, LT.sub.2 respectively associated with the caller and the responder. Monitoring memory LP, registering the progress of a call in a corresponding phase thereof, defines up to 10 different states in the establishment of a connection; in the event of a toll call, state No. 10 is followed by either state No. 11 or state No. 12, depending on whether the charge is to be debited to the calling or the called party, wherever a supervisory unit emits a rate pulse.