Maybe a standarized national system to report spam, or maybe even as part of the cellular protocol? I never heard of such a system deployed nationally, but I'm wondering if it could help.
Most of the time when a spam number calls me, I can find it through spam reports on 3rd party websites by googling it.
No, it seems most spammers here use cheap SIMs without spoofing (which seems to be what OP is about). They even leave voicemail messages asking to call back.
But spoofing is also something that should be fixed. I know it's difficult because of VoIP and backwards-compatibility, but it's not impossible either.
You're forgetting that 1) carriers have near-zero engineering capability to fix this and 2) don't actually have an incentive to prevent spam/fraud because fraudulent traffic still pays them money.
This is not about stopping fraud, this is about preventing "grey routes" that do arbitrage around tariffs and bypass carriers' outdated business model.