Google Talk - No XMPP Server to Server Functionality
I was poking around on the Google Talk website and found this Help Center item.
How do I use Google Talk to communicate with non-Gmail users?
It isn’t possible to call or chat with non-Gmail users through Google Talk (but we’re working on it). You can email any of your contacts by clicking the envelope next to their names in your Friends list, but if you want to talk to your friends live, they need to be Gmail (and Google Talk) users too.
You can invite your friends who aren’t Gmail users to download Google Talk. They’ll be sent an invitation to create a Gmail account at the same time. Just sign in to Google Talk, and click ‘invite’ next to your friend’s name or click ‘Add friend’ at the bottom of your Friends list. Then follow the prompts to email an invitation to his or her email address.
Well thats just tit useless when your going to use XMPP, isn’t it?