Abstract: The method assesses the suitability of customer telephone lines (12, 13, 14) for data transmission. The method includes selecting a telephone line having tip and ring wires by means of a computer (30) and switch (15), and electrically connecting the tip and ring wires together at a test access (29) adjacent one end of the selected line to produce a common mode configuration. Single-ended electrical measurements are performed on the wires in the common mode configuration by a measurement unit (27) connected to the test access (29) to determine an electrical property of the wires from the measurements.