I can't actualy connect at all with jmIrc. As some people reported, I'm having some similar troubles to connect.
I tried standard port 6667 but also some ports >1024 both failed.
I noticed with another app. that I need to use a setting that doesn't exist actualy.
For Blackberry Bold 9700 OS 5, we need an option to choose if we want to connect thru:
TCP/IP : Use the APN settings (in my case doesn't work at all even with ssh)
WAP2: Same than above
BES: is for Business Entreprise Server users, mostly big corporate (not my case)
BIS: is for most users provided by carrier and it's the one working in my case (at least on ports >1024)
Don't hesitate to ask me here if you need tests or debug logs or provide me an email.