A private branch exchange (PABX) with an integrated mobile part for controlling cordless terminals (HS) is established, which can be operated from base stations (BS).The private branch exchange (PABX) contains freely configurable interface modules (I/F) for wired (DE) and cordless (HS) terminals, which can be operated from a base station (BS). A central control unit (PABX-CPU) is provided to control all call handling and service feature control tasks, and a subordinate control unit (Mobile-CPU) for call setup and switch-off control of the cordless terminals (HS) in accordance with a set of assigned call numbers. The control units (PABX-CPU, Mobile-CPU) and the interface modules (I/F) are connected with each other through a bus system (BUS).