Note: This is a US (and Canada) based answer. Things can be quite different elsewhere, especially if you need to interact with landlines. It looks like the rest

Note: This is a US (and Canada) based answer. Things can be quite different elsewhere, especially if you need to interact with landlines. It looks like the rest of the world is probably going to end up adopting some version of STIR/SHAKEN eventually but adoption is going to be limited for now if you need a phone number that doesn't start with +1. You can block based on STIR/SHAKEN attestations, and have a blocklist of calling carriers, but you'll have to run your own PBX and SIP trunk to do it. That's not too big a lift anymore, at least. You would probably also have to block all C attestations and unattested calls though, which is going to lose international calling and some older domestic phone systems. So - yeah, you can kinda do this now, and will be able to do it more in the future, but keep in mind that carrier level blocking like this is the equivalent of null routing entire ASNs.