http://jmirc.sf.net/beta/jmIrc.jad
Go there in your browser on your phone, install and run it. Set up a profile and then go to Advanced under menu. Scroll to the bottom and select BB WiFi if you're connecting using WiFi, or select one of the others if you're connecting over the air (your cell phone service). It works for me on OS6 (.424) and it worked on OS5.