There are now a lot of XMPP extensions to fit the mobile messaging use case better (usage of push notifications instead of a persistent TCP connection etc.), and at least two clients using them: ChatSecure (although the push server seems to be broken currently) and Monal.
Due to the lack of anyone to chat with on XMPP, I can't really speak to the day-to-day usability unfortunately...
Due to the lack of anyone to chat with on XMPP, I can't really speak to the day-to-day usability unfortunately...