One of the improvements in iChatAV 3.0 (shipped with Tiger) over iChat AV 2.0 (shipped with Panther) is its support for Jabber, which allows you to indirectly communicate with other
IM services like MSN and Yahoo. There’s a nice tutorial on how to get your iChat to talk to MSN at All Forces. I followed the instructions on the All Forces site to set up my iChat to communicate with
Yahoo. The trick is to locate a public Jabber server that supports Yahoo. Although there are plenty to choose from here, not all public Jabber servers that support Yahoo work well with iChat. Several
allowed me to send messages to Yahoo from iChat, but not to iChat from Yahoo. I was about ready to give up until I tried jabber.org.uk. Now I can use iChat for both AIM and Yahoo instant messaging.
iChat has better integration with other Mac OS X apps. For example, when you’re logged into both AIM and Jabber–>Yahoo in iChat, the little green dot appears next to emails from online buddies in Mail.app. This has always worked with AIM and .Mac IM users, but now thanks to Jabber support in iChat, it also works with Yahoo buddies.