I think Canada's system does this, though it might only be a couple seconds. I recall being able to stay on the line ~10 seconds or more and still retain the call. If you have the person on the other side of the phone holding the card and looking at the phone number, being instructed to call it because of some urgent fraud, they're almost certainly going to hang up, and pick back up within a ~5 second window.

And if they don't, no harm, no foul (to the scammers)