I just rediscovered this IM client for my 7650 called TipicME. It's a J2ME-based Jabber client that is really well done and unbelievably FREE.
I saw it before but I'm not sure why I decided I didn't like it, but it's really great. Instead I bought the IM+ app, which works, but the UI is horrible: Each message is a separate screen and it makes having a conversation really difficult. As you can see from the Tipic screen shots above, they've done a really good job at duplicating a normal IM interface and it works well. It also communicates with all the IMs: ICQ, AIM, MSN, Yahoo and Jabber.
There are some downsides, like there's no sound notification (besides a little beep) if you get a message, and it's relying on Jabber servers which can be flaky in their connections to the big services. But other than that, there's not much wrong with this app. I'm sorta wondering if I wasted $30 on the IM+...