Comment by eridius

The gist explicitly claims that's not possible. Specifically, it claims that there's no way for the Saudi teleco to distinguish encrypted phone calls from encrypted messages, and since you can send encrypted messages to Saudi users, there's no technical reason why you can't also call them. The implication is that if WhatsApp did allow the calls, the Saudi telecos might block both calls and messages (since they can't distinguish them), and so WhatsApp disallows calls to avoid provoking them. And the OP's point is that WhatsApp should detect whether the user is actually in-country and allow the calls if they're in another country (since the Saudi telecos won't matter there).