There are a number of Java J2ME IRC clients available for mobile devices. The problem is, Java applications take a long time to load as well as huge resources.

mIRGGI is a native Symbian 9.1 based IRC client for Nokia S60 3rd Edition mobile devices in Beta.

Here are some of the features currently supported:

-connecting to one server
-joining channels
-query windows for private chatting
-10k per channel/query backlog
-jumping to desired window with numpad
-ident daemon
-UTF-8 decoding
-T9 support
-usually needed commands implemented
-the font is small
-small memory requirements
-settings for autojoin and autoquery on connection

Download from here