It seems to me that phone companies can detect that, but they don't want to reduce the number of calls, do they?
This is mostly a US problem though. In Europe, the operators tend to be more strict on this, AFAIK.
And that's an awful lot of work just to cold-call someone to try to sell them insurance or whatever.
This has happened multiple times before, at least two separate incidents have made the news.
I'm sorry, this just sounds far-fetched to me. History seems to have shown that when hurdles are just a little too high, the spammers just don't bother.
I currently use the "Should I Answer" app, mentioned below, which is about as good as it gets in terms of pissed off people working together to fight the good fight I think.
However, all of this crap is still jist a bandaid for a lack of our governmental ability (at least in the U.S.) to hold phone utilities accountable for the illegal use of phone numbers.(1) Fine the phone companies hard and the problem goes away.
1. https://www.consumerreports.org/consumerist/phone-companies-...