What should be done is something else entirely. Apple and Google should offer, as part of their standard software, a personal "phone robot". When you get a new phone, you spend 15 minutes recording various phrases, and from that point on you just have the robot answer for you.

When the robot talks to these spammers and telemarketers, it will try to keep them on the phone as long as possible. A minute would be good, 10 minutes would be better. As the spammers tried to avoid this, Apple and Google could improve the robots to counter.

And, within a few months of this, at most, that industry would just be dead. It can't afford to spend a half hour on each call trying to determine if they've got a real live knucklehead who will start sending cash to Nigerian princes, or just bad software tricking operators who don't speak English as a first language. Their margins would drop, their need for more sophisticated AI to try to determine if they were talking to a real person or not would skyrocket, etc. It just wouldn't be economically viable to continue.