Try jmirc again. Get version 0.91, or if you can, 0.82, these have been stable for me on my blackberry.
Other versions are not so stable, there is a pesky bug for Blackberry users that the author may have solved by now, therefore maybe the latest version works, otherwise, if it does not ask him to send you 0.91 or 0.82.
Send all reports direct to the developer through his website,
http://jmirc.sourceforge.net/