A termination device for a telephone line of a wire based telephone system, said termination device (30) comprising: a high pass filter (39) for separating signals within a frequency band used by a high-speed modem (13) for data transmission; and impedance means (53) connected to the high-pass filter (39), wherein said impedance means (53) has an impedance which matches the impedance of the telephone line in the frequency band used by the high-speed modem (13).