Earlier quoted context omitted.
It's not apparent from the article if phone calls are blocked. It's probably not cheap, and it's certainly easy to track, but you can run data over international voice calls. Probably works better on a real landline, but should work a bit over mobile too.
You'd have to know a modem pool to call and have an account there, I wouldn't even know where to start. Especially if I was already cut off from the Internet.
However, if you know someone technical out of the country, you can call them and ask them to set something up and get you the details. (Or you can't call them, and there you go).
If you're talking with people on things like Signal or WhatsApp, where phone numbers are user ids, you automatically know their phone number to call them in case the chat service is unreachable.