Abstract: A device for interposing in a telephone service line for testing the service line and a telephone network attached to the service line. Included is a first circuit for testing the service line, a second circuit for testing the telephone network, a third circuit for providing a normal connected between the service line and the telephone network, a fourth circuit for generating a reset signal on the service line, and a fifth circuit for testing an individual handset. Connectors are provided for connecting the device in circuit between a telephone service line and a telephone network. A multiposition switch is included for switching between the first through fifth circuits.