[jimktrains2]

I've never implemented it, but from a user standpoint, there aren't any widely-available services that people seem to use. gchat appears to be shutting their endpoints down. Facebook shut theirs down in 2014.

People got familiar with email because their ISP/employer provided them with an email address. Eventually it became a thing on it's own. Chat was never like that. There was always one service you used, and all your friends used. Now that's gchat and facebook chat.

[larma]

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.