i want to try blackberry just for its Black Berry Messenger (BBM) app. i have an iphone so if i have an unlimited data plan and i IM through yahoo messenger, would it be the same as blackberry messenger ? if i have 5 friends and they have yahoo messenger too, i can easily connect with them via yahoo ? i just don't understand what is so special about BBM ? can't you just IM through any other app that your friends have ?