An abusive customer is an opportunity for some rather frank feedback. Rather than cut them off I would have the agent say ...
'Sir, I can see you're quite upset so I'd like to pass you over to one of our senior complaints managers who will look into this for you and see what we can do to put this right'
Passing the call to an agent trained in exception handling can often lead to some interesting insights, customer retention and can even avoid costly legal action in some cases.
I remember one abusive screamer who, it eventually turned out, had found his private financial details regarding a juicy mortgage claim had been revealed in error to his wife - whom he was currently divorcing. He worked for an FSA/ICO regulated firm of accountants in London and was not only livid but downright litigatious.
If the agent had have hung up we no doubt would have had a very costly damages case on our hands. As it happens he was placated.
The moral? Never let a frontliner hang up on a screamer! At the very least it should escalate immediately to a TM before it gets out of control, and preferably to senior staff with a good understanding of exceptions handling.
-TheITGuy