Just to be precise: Google and Facebook did not shut down their xmpp servers, they just disabled the ability to connect to them via xmpp clients, to make sure everyone uses their web clients, so they don't loose any data they could've collected otherwise...

The original Google Talk ifnrastructure is still up and running and clients can connect to it using a protocol derived from XMPP (basically a subset XMPP converted to protobuf) and use it to message devices (Android uses it push messaging, but technically you can also send messages directly between devices). It's not directly used for text messaging though.