Abstract: Disclosed is a portable fixture which can be employed in simulating and testing the various functions of a conventional payphone. In general terms, the fixture includes an umbilical cord which can be removably connected to a payphone's motherboard. The fixture further includes a receptor for accepting a phone line, as well as electrical connectors for removably accepting the existing handset. When connected, the keypad of the fixture serves to override the payphone's keypad. Thus, when connected, the fixture mimics many of the operational functions of the payphone. Also disclosed is a diagnostic circuit within the fixture. The circuit is specifically for use in testing the operational status of the payphone's escrow relay device. The circuit is plugged into the payphone's existing escrow relay by way of an electrical connector associated with the fixture.