The Agent training cord allows two headsets to operate on one telephone for training/monitoring purposes.  
Both headsets can listen, but only one headset will have a live microphone.  The other microphone is muted.

Designed for side-by-side training sessions when both users have corded headsets with the same variant of QD.
Two headsets plug into the top of the cable while a single bottom cable connects the training cable to your phone.
Includes an in-line mute switch to give you control of which user can speak on the call.