Main culprits in this nonsense are the phone companies who profit off it at their customers' expense. It's basically like cable tv where you're expected to pay to watch commercials.
So you want the Phone Companies to get involved in policing the content of the calls that are made? When you order a phone line, should the Phone Company put you through a detailed and exhaustive screening process mandated by their lawyers because they've been sued for the contents of calls that some of their customers have made? Should they then be allowed to monitor your calls for violations of their AUP? I mean, i…
The real issue is that phones were ever allowed to ring in the first place. They should all just leave a message which should then be stored until a I chose to listen to it. Then in the future, calls from that number could be allowed.
In addition the phone company could allow you to preunblock certain numbers, such as those from your schools and hospitals.