Get the caller committed by spending time. Damn, my PC seems to take forever to boot, okay, now what? Oh, oops, someone's at the door, can you hold? Ah now I'm back, could you repeat all that, I forgot while dealing with a friend at the door. So I type what where? Oh wait, I need to use the bathroom.
At which point the phone gets set down and left there. Even when the caller finally hangs up that line will stay open for IIRC 30 more seconds as long as you don't hang up at your end, yet you won't hear the snarling and cursing.