Add the Discover D300 Training adapter and you'll be able to connect two wired or wireless headsets to a single desk phone for supervisors to listen in on calls and train.
The D300 Training Adapter works exceptionally well. The D300 adapter connects the Main headset and the Training headset. To listen to conversations on the Main headset the user with the Training headset must press the button on the headset [as though the training headset is connected to a lifter]. The call is automatically connected to the training headset when this button is pressed.