Do you play an automated message when the tech comes on the phone? How many phone service technicians will actually sit there and wait to be connected to the actual user?
Since call center employees commonly have the ability to perform call transfers, I can only imagine they have the ability to hang up on calls. Otherwise, I imagine they could simply transfer the call to an invalid extension to "hangup".
The other good one is cancelling a contract where they ask you to wait and simply keep your line open and don't let you make any calls for the next 20 mins ... always a joy. AFAIK there's no way on our phone system to force an incoming call to terminate.