These messaging apps are worse than... well, I don't know. This is as bad as it gets. Bicycles maybe? Incompatibility, fragmentation.. the worst thing you can have for application that is supposed to be used for communication.
At least Telegram has an API and a documented protocol... It could have been a lot better, but WhatsApp is a reminder that it could have a lot worse too.
In the 00s, we had multi-IM clients like Trillian, Gaim/Pidgin/libpurple, Kopete, Telepathy, etc.
Now, there's so little work done in reverse-engineering IM protocols. It's really sad. Part of this is because Sean Egan got hired by Google to work on Hangouts, so he's out of the reverse-engineering game for good, and it's sad that nobody took up the mantle from him.
Depends... in eastern-ish Europe it was ICQ only. That was kind of fine.
What I don't get is why mobile carriers still charge for SMS. They could have all deployed their own SMS apps with ads/premium where you could write messages for free. Some did that, but rather badly I think. They just let that market go.