I think you're right, but we're looking at this from opposite angles. We can never stop people trying to make spam calls, because human nature. At the same time, I don't think it's a desirable design goal to have a communication system that isn't open to everyone. So we must address spam on the receiving end. That's exactly what email is doing, in a decentralized way, pretty effectively in my opinion.

Now why are cell carriers dragging their feet even for basic problems like caller ID spoofing, which have been solved in the tech industry for decades now? 10 years ago, if I could have switched to any carrier at all that blocked spoofed calls, I definitely would have. But no company offered that service for the reasons I mentioned, and now it's too late and people have mostly given up on voice calls.

If email were a government-bolstered oligopoly and we all had to rely on Verizon's in-house engineers for spam filtering, email would be good as dead too. Email is certainly not perfect, but overall I think email's open model has aged much better.