An interface device allows communication between a first telephone terminal, a second, wireless telephone terminal, and a telephone network. The device includes a transceiver for transmitting and receiving wireless signals to and from the wireless terminal, the wireless signals including authentication data identifying the terminal, such as the data carried by a SIM card. A data processor processes the authentication data. The processed authentication data can be transmitted to the fixed network. The first telephone terminal is connected to the interface such that communication between the first terminal and the network can be enabled by the authentication data received from the wireless telephone terminal. The wireless signals may be carried over an "ad hoc piconet" system.