With the barge-in feature, admins/supervisors can interrupt or barge in during a call between agent & customer.
Intellicon provides you three variants:
Listen (You can only listen to the conversation)
Whisper (In this scenario you can talk to agent only, mostly used for new agents training’s)
Barge-In (Three party conference, in this you can talk to both agent & customer)
Below video can help you with its configuration:
How to Add Sip Account For Administration