QuickTap IFB connects between telephone and handset for quick access to audio from any telephone system. Simply unplug the handset coily cord from the base of your telephone and plug it directly into the QuickTap IFB, then, using the supplied cable, connect the QuickTap IFB to the base of the telephone. The 600 ohm male XLR lets you take audio from the phone line and route it into a mixer or headset amplifier. You can also plug an IFB earpiece directly into the 1/8" mini jack. However, keep in mind this is a passive box with a 600 ohm output; the earpiece should have an impedance greater than 600 ohms to get usable output. Both audio output jacks contain a nice mix of the audio coming from the phone line and the handset audio going into the phone. Any conversation over the handset is sent over both audio output jacks. Or you can leave the handset disconnected and just hear audio from the far end of the call. The QuickTap IFB does not work with cellular telephones or any telephone with a keypad in the handset.