Unfortunately, I am not familiar with writing operating systems. But this seems, superficially, not complicated at all.
You can leave it up to the user to mark countries as "XYZ", with some self-defined warnings. This seems about as complicated as displaying a caller name. And a blocking function is already a thing, but only for specific numbers.
You can simplify it even further and let the user block numbers in the format +44*, where * is any series of numbers. I don't get why you need to be a nay-sayer for a feature this trivial.
However, I would like a warnings and a menu option if possible (Samsung has this apparently) to make the user aware that the feature exists and that the problem exists (scams are obvious, but one-party consent is not). Nudging the user towards better privacy options is effective.