That won't work, because with current technology it's impossible to tell where the calls originate from.
I'm not defending the telcos for dragging their feet on this issue, and I'm also not opposed to regulation, but there's a technological aspect to this problem which I think you're underestimating. The technology needs to be fixed before any regulation will be in any way enforceable.
The technology fix isn't something that can be implemented "overnight" either. If I'm understanding correctly, existing signing was implemented in hardware, because at the time it was implemented, that was the only way to get the performance necessary, and in the US most of the hardware the phone system runs on is legacy hardware. The solution has to be provably secure, support existing network hardware, support existing consumer hardware, be upgradeable, federate to avoid centralization, be agreed upon by all the telcos, be approved by regulators, and finally, be deployed without downtime. That's simply not going to happen overnight, and it's worth it to take the time to do it correctly rather than cutting corners on any of these steps.
I'm not defending the telcos for dragging their feet on this issue, and I'm also not opposed to regulation, but there's a technological aspect to this problem which I think you're underestimating. The technology needs to be fixed before any regulation will be in any way enforceable.
The technology fix isn't something that can be implemented "overnight" either. If I'm understanding correctly, existing signing was implemented in hardware, because at the time it was implemented, that was the only way to get the performance necessary, and in the US most of the hardware the phone system runs on is legacy hardware. The solution has to be provably secure, support existing network hardware, support existing consumer hardware, be upgradeable, federate to avoid centralization, be agreed upon by all the telcos, be approved by regulators, and finally, be deployed without downtime. That's simply not going to happen overnight, and it's worth it to take the time to do it correctly rather than cutting corners on any of these steps.