I have a blackberry unlimited data plan, and want to continue using Trillian on my 8700G. Will this be a problem? Am I going to be charged for that? It doesn't make sense! Isn't it just another internet function I should be able to use when on EDGE or gprs or something?

Yes i dont believe that uses text messages so you will be fine with your unlimited data.

I assume your on tmobile. Go to tmobile.com and log onto your account. You will then be able to tell if your indeed using text messages or not.