meebo - gives you a multi-protocol instant messaging application for the iPhone. meebo is item three in the third ‘web’ web row at Best Phone Apps. Reports differ on the usability of meebo on the iPhone, and all we know is that it works with iPhoney. The meebo about page says:

meebo.com is a website for instant messaging from absolutely anywhere. Whether you’re at home, on campus, at work, or traveling foreign lands, hop over to meebo.com on any computer to access all of your buddies (on AIM, Yahoo!, MSN, Google Talk, ICQ and Jabber) and chat with them, no downloads or installs required, for free!.

iPhone compatibility uncertain.