Stay on the line until the call can be traced. Of course now that can be done before the caller gets the first syllable out.
I wonder how many terrorists watch the movies and take it to heart. Probably have their 60 second timer on top of the phone -- hanging up right at 59 as the person on the other side laughs. Of course you have to BELIEVE the other person -- which is how Sniper Muhammed avoided capture for so long.