In case you haven’t heard, Google has ‘released’ their IM system - it’s just a Jabber server, though. There are a couple of review around, and I haven’t read all of them in that much detail.
It requires a Gmail account: I have plenty of invites if you want one, just email me.
The settings you need are (I use Adium, your client’s names may vary):
Account Type: Jabber - I couldn’t get a connection without this, some have said opposite.
Jabber ID: your.account@gmail.com
Password: ••••••••
Connect Server: talk.google.com
Port: 5222
Security: Use TLS Encryption (if possible)
Others have said that any person with whom you have shared Gmail will be automatically added to your buddy list. I haven’t had anyone added to mine, but then I don’t really Gmail many people.
I’ve also created accounts with the other IM players, you can find them under the Contact page.
