For consumers at least, it's the law in the EU. Every phone network has either a pricing document or a webpage where you can type a number and it tells you the price, and if you were charged something that isn't that price, I guess you could demand a refund, and escalate to a court if the refund wasn't forthcoming.
Note that these documents frequently list some numbers at ridiculously high prices (eg. €25 per minute), presumably to deter such fraud.
I think the problem with that is that these schemes rely on the phone network being ridiculously insecure. The scammers send a surprise bill to your telco, then they pass it along to you.
It wouldn't surprise me if the list only applies to consumer plans, or (as you say) high-balls stuff in certain countries.
I wonder what would happen if the telco would say "we wont pay the bill, since we believe it is fraudulent".
They wont "lose much" if some fraudulent telco from third world cuts them - the numbers dont work anyway.
And what can the scammers do? Try to sue an US telecom? If they reveal their true names, then the embassy knows where to send the "operators" who will solve the case for good.
There is normally a long chain of intermediate telco operators between the fraudsters and the US operator. Some of those intermediate operators are large and have a lot of legit calls. Each operator adds their profit margin on and passes the bill to the next. So no operator has any incentive to police this stuff, because they all profit from it.
Note that these documents frequently list some numbers at ridiculously high prices (eg. €25 per minute), presumably to deter such fraud.