All in one IM

No native apps that I know of will do that, at least not right now. I used JiveTalk on my BlackBerry which was awesome. The developer is creating a version for the iPhone but right now you can only use web apps. If you follow the link below in your phones browser you can use a very boring version of JiveTalk.

http://iphone.beejive.com

I still hate the fact that you can only run one program at a time. This really makes other phones look so much better compared to the iPhone. My BlackBerry could run multiple apps at a time and even had a task switcher. I sure hope Apple makes this same functionality appear in newer versions of the firmware.