Just make it so you can opt-in to an exception and nobody will care. If you live in the EU and want to call me (as if you know my number, and have reason to call me) you won't have a problem. If you live in Russia you might have a problem - but I have no reason to think anyone in Russia will ever call me so I don't care. The few people who do have friends in Russia can add an exceptions and those exceptions are not enough for spammers to bother operating at all anymore.
I'd suggest it be optional on a per-customer basis, perhaps with a whitelist.
E.g., the only international calls I ever want to receive comes from family members' cell phones when they're traveling.
I'm 100% okay with blocking all other international calls. If something is that important, they can send me something via mail, FedEx, etc., or send a message courier to my house.
This already works: a staple of these threads is some European user who has sender-pays service expressing surprise that this is a problem because it’s so rare in their experience. Those countries can still receive international calls.