I don't understand why people are having a problem understanding the difference between AIM, or something similar, and BBM. BBM is basically like a free text message to someone else that has a blackberry.
With AIM, if your not logged on then your not getting the message, simple. Even if you send them a message for when they get back online, God knows when that will be. With BBM it is like a text message, you don't need a screen name and you don't need to be logged on, you just get it like you would a text.
I would love this because I know a lot of people who have iphones. Instead of wasting my text messages, that I have a limited amount of before I start paying more, I can use my data instead (which isn't limited like my texts are).
Does this not makes sense?
Edit: I don't know what push IM is, but I wouldn't want to log on every time I wanted to see a message. It would take more time (I know probably not much more) but then more people could start talking to me online which I may not want.