C019 Telephone Phone Line Network Cable Tester Butt Test Tester Lineman Tool Cable Set with Connectors and Joiner On/Off and hangup buttons. FSK/DTMF dual system Caller ID Easy for the lineman to check your telephone line fault. Come with Three type of line plug,easily connect to the phone line. This set offers Last number redial, On/Off and hangup buttons, so the lineman can check your telephone line fault.