If I buy a new phone, import my global contact(s) to it and do a search of who has what. 80+% are on Whatsapp (with the only big exceptions being US and China nationals), 12% are on Viber (with more being from Eastern Europe and Korea, however without exception every single Eastern European is ALSO on Whatsapp), 5% on Wechat (all but one Chinese), 5% on Duo, and about 2% on Zello, 1% on Signal, 1% Telegram,1% Wire, and less than 1% Skype.