I'm shocked that a startup with a similar approach to WhatsApp hasn't made a reasonable rigorous application yet.
Equivalent to cc'ing the NSA.
Whatsapp - broken encryption Google Hangout - NSA Texts - NSA (and others) Facebook Messenger - NSA iMessage - probably NSA, though I don't know.
and so forth. Most commonly used text services are woefully leaky.
It's rather sad, given that with practically any other application (Line, WeChat, GTalk, Skype) you can talk via phone, tablet or PC, and with WhatsApp I have to message my friends with a tiny phone screen while my wonderful desktop keyboard and dual monitors sit there laughing at me.
Unfortunately, Threema is not FOSS either.
The apps developed by Moxie Marlinspike also seem good to me, I've used RedPhone and it's pretty nice. The texting app sends SMS, though, it doesn't go through the Internet, so it might not be what you're looking for.
Silent Circle's mail service was shut in the aftermath of the Lavabit shutdown. Why shouldn't that happen to the messaging service? What's the difference?
if jabber worked, we wouldn't be talking about whatsapp/hemlis/threema.