WhatsApp covers a lot of the remainder. When I worked at a job with frequent contact with international guests, the vast majority of people from Africa and SEA, and a good portion of those from Latin American and MENA, were on it. In fact, the first time I'd heard of the app was from them. This was about 10 or 11 years ago. It might have changed since then, as Facebook has for us, but Zuck's empire (read: illegal monopoly) has been dominant globally.