There is a super easy way to absolutely fix the spam caller problem.
Charge 1-cent to terminate a call on the PSTN. Just a 1-cent fee every time you place a call, whether it goes through, is answered, or is an invalid number. 1-cent to try to call a number.
Put that 1-cent into the Universal Service Fund (and reduce the flat-per-line charge system we now have.)
This 1-cent per call attempt would probably eliminate the per-line Universal Service Fee we now all pay. So it would be revenue neutral.
But this penny per call attempt would totally flip the economics of spamming. There would be a cost of $100 for every 10,000 call attempts. From everything I can read, the “expected value” to a spammer from 10,000 call attempts is about $1~$10. Suddenly you can’t make a profit by spamming. End of game.
All of the mechanisms to charge the 1-cent termination fee are now in place already. It’s not a hideously complicated system like SHAKEN/STIR. It could be implemented this year.
This 1-cent fee might never be seen by most consumers. AT&T could still offer unlimited calling. Behind the scenes they would pay the 1-cent fee to terminate calls (just as they now pay other termination fees.) But AT&T would have every incentive to cut off a customer who is originating thousands of calls using their “Fair Use” policy.
Yes, really, the spam problem fixes this simply.