I am intrigued. What messaging app do people in the US use? SMS? Or iMessage? What cross-platform messaging is the most common in US? I mean to ask "used overall" and not by a particular age group.

Here in India I used to think it's only WhatsApp pretty much then I realised there are many apps which have substantial user-bases e.g. hike messenger (hike.in). I was surprised that Viber still has decent number of users in India and then of course there is Fb Messenger.