JiveTalk works great on the 8800c. I do not remember the email address to get the beta version of it. This software is currently only in beta so it is free right now but most likely when full version is release it will be pay to get app. But honestly it works great and I will pay if it goes to that. Search the forums and I am sure you will find the email to get the JiveTalk beta.
JiveTalk really is the best IM program on the market until the carriers open up the service books for the Blackberry clients. However, the Blackberry clients are not all integrated like Jive. Jive is fast, reliable, and works solidly. I hope they do a one time charge for it rather than a subscription model once they move out of Beta.