although messages on OSX can do this without an issue, the messages app on iOS is strictly for SMS and iMessages only. That means jabber, in messages, on your iphone, will not work.
There are a number of applications that will support Jabber on your phone and you will have to use those applications to talk.
I personally have use BeeJive and also Google Hangouts for iOS to get jabber working on my phone. Most clients will have their own native application that supports chat features.
But again, you will not be able to setup jabber in Messages, like you did in Messages on OSX.
I know it is a little confusing.
Not confusing, at all; a bummer, but not surprising.
I have both Beejive and Hangouts on my iPhone. I also have IM+, too. Don't think any of them will look like the Messages interface in that I would need to swap back and forth between separate conversations, while Messages will displayed all the messages on one screen, even if they are separate.
Thanks for the reply!