Terminal unit for network with circuit switching and network with packet switching

The device has a data transmitter (SLT) for sending and receiving in the circuit-switched network (LVN) and for connection to the circuit-switched network, a universally applicable device for automatic data processing and sending and receiving in the packet-switched network (PVN) and at least one data terminal equipment (SLT) associated with the transmitter and switchable between modes for connection to the circuit-switched and packet-switched networks. Independent claims are also included for the following: (a) a data transmitter, especially for voice and/or packet data (b) and a data terminal equipment.