I work at a big government organization. Every department has its whatts group.
I know a guy at my state government cabinet. He has several whatts groups (even one with the governor himself).
I know a gentleman which is a judge. He has a group with his partner judges and one with his staff.
My point is: if whatsapp usage is so pervasive at other countries as it is at Brazil, it will soon, by (physical) social network effect, dominate USA.
The alternatives:
* Facebook Messenger: too slow. Only one friend of mine uses it.
* Telegram: looks and feels like a whatts clone. Some people here seem passionate about inviting friends, but most people I talk about fail to see any advantage in using it. Some people hate it. As a plus, it will SPAM all your contacts when you sign up.
* Google Hangout: even I can't figure out what this is. Is this SMS or a messenger application. Now my phone has another application called Messenger (from Google). Confuse. No one I know use it.
* SMS: too expensive.
* Apple Message: only Apple users can use it. People prefer whatts because everyone is there.
* Zoiper: got traction, but whatts voice messages killed it.