I have whatsapp, though my free year is nearly up so I'll just knock it on the head and tell it to jog on. I know a few who use Line, which has a massive library of emoticons available (albeit most for purchase).

Skype is butt annoying because not only does it mess about with messages, but when you've read everything on one device, and move to another, Skype decides you haven't read everything and that you should read it again, from the last time you were online on that device, meaning you could get notifications for month old messages. I really annoys and I end up not using it.