You need the F1044 key assigned to the supervisors set.
The supervisor must then be in ready, break, or work mode and press the Monitor key.
They will see MONITOR NUMBER? in the display.
The supervisor then enters either the agent ID + # or 0 + the extension number + #. The agent or PBX number can be entered.If the agent is on a call the supervisor will be able to silently listen in. If the agent is idle I believe the key will chime once the agent goes into a call.
To barge in the supervisor presses the Monitor key again and they will see BARGE? in the display. If they press 1# a 3 way conference will be set up.