It's a real shame private messaging has ended up being almost exclusively closed-source without any kind of open API.
In the EU at least WhatsApp is being forced to interop with other messaging apps. I believe it's being rolled out at the moment.
The world still runs on email.
How did we let this happen? We used to have open protocols, apps like Pidgin that would bring multiple chat clients together under one interface, IRC, Skype P2P, etc. etc.
Was it spammers that caused this mass migration to ever more closed platforms?