JK Audio QuickTap IFB - Manual (Page 3)

3
Operation
The audio output jacks provide a mix of both
sides of the conversation. In other words, as
you talk down the handset your speech will
come back on this jack mixed with the audio
from the other side of the call. You do not need
to connect the handset to QuickTap IFB if you
only want clean audio from the phone line.