Well the telco doesn't exactly know who is the caller. They only know through which carrier the call came from - and they in turn charge that carrier per minute

Well the telco doesn't exactly know who is the caller. They only know through which carrier the call came from - and they in turn charge that carrier per minute of inbound calling. It only allows them to pinpoint it to a specific carrier, however the spam calls often use the same carrier as the legitimate calls, and this is where the trail ends. Having an end-to-end chain of ownership for the call that can be verified cryptographically would help a lot, since even you on the receiving end should be able to verify this provided you have the appropriate software on your phone. Bad callers using Mechanical Turk would be a minor issue - you won't even have to sue, just get in touch with their telco and they'll shut down their access for violation of ToS (in fact a lot of telcos already prohibit using their consumer-grade plans for business usage, even if not spam). Unless you're paying those Mechanical Turk contractors a lot nobody is gonna bother setting up extra lines to make those calls, and nobody is gonna pay them a lot of money because the only way this spam works is because it's dirt cheap to spew out those calls with the current situation.