XMPP is used for Facebook Messager, Google Talk and even WhatsApp. Just WhatsApp adds proprietary options to it and does some weird key exchange on first signup

XMPP is used for Facebook Messager, Google Talk and even WhatsApp. Just WhatsApp adds proprietary options to it and does some weird key exchange on first signup. So there is e.g. no chance to log in from your computer or simultaneously running it on multiple devices. You are right, a permanent connection isn't that great on mobile phones, but as a custom XMPP service you could just use push technology like every other app, too. That's what e.g. Google and Facebook are doing. Beejive and IM+, two common mobile IM apps with XMPP support, are doing this, too. The only downside is, that since they don't want to store you credentials, you have to run the app to reconnect to your XMPP server and delegate that connection to their push servers. This is just a bit annoying when either jabber.org or their servers have connection errors.