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Mibbit is a web based IRC client that works on your iPhone or iPod touch, although not a iPhone optimized webapp, it allows you to access the world of IRC chat servers.

You can connect to multiple servers, manage auto-connects to log you in and join your favorite channels automatically.
Mibbit parses links, nicks, smilies, channels and supports private messaging users, or chatting together in public channels. It also has typing notify to let you know when people are typing a reply. Try with TestiPhone