Beejive has produced a very nice mobile instant messaging client for iPhone, BlackBerry, and Windows Mobile. It supports a number of IM protocols.
I tried out Beejive on the iPhone, using XMPP (the Internet Standard eXtensible Messaging and Presence Protocol). The protocol support is good, and the user experience and interface are excellent. I liked the way that the XMPP Roster (buddy list) and chat screens were integrated together. It looks good and is very easy to set up and use. The $15.99 price is attractive.
... Steve Kille