The PI9 takes a signal from a standard telephone jack and,via transformer isolation, connects to a pair of RCA jacks, or a stereo 1/8" (3.5mm) jack. The isolation keeps the output signal separate from the telephone line, and will not keep the line open unless the internal jumper is moved. Applications for the PI9 include broadcast, conference rooms, phone training, or wherever a phone conversation needs to be recorded or heard over a PA system.