Hi,
I really feel that this is something you should pay for.
If you cannot afford WebMessenger, get one of the many cheaper instant-messaging clones now Blackberry compatible instead:
http://midlet.org/category.jsp?parentLevel=222
(Load this URL on your Blackberry and do an Over-The-Air download. IM+ is one that also works)
Although WebMessenger has the superior user interface in my experience, the other programs I tested were more usable than WAP instant messaging and could suit your needs at your budget. (I like WebMessenger's split-screen full-duplex chatting that takes little effort compared to other instant messaging solutions ... I just type messages and hit Enter, type another message, hit Enter, and so on, without ever using the thumbwheel .... while in a splitscreen the incoming messages show up)
And there's now an open-source free ICQ client called BlackChat ICQ at:
http://sourceforge.net/projects/blackchat