I'm not sure how the phone system in the US works, but here in the UK a good tip is to hit the recall button, that should give you dial tone and put the person/robot on hold, then hang up the phone, the exchange will ring you back so you can take the call on hold, don't answer it, after a few rings it gives up and the call is dropped

Although your idea sounds pretty good for live cold callers too.

Cheers

Cris.