May I ask where you're located, because personally, I had a Blackjack before the iPhone, and with unlimited data i was paying 20 more for data on a phone not as great....so I don't know, but the iPhne actually made my bill lower than it was before I got it, check the plany, &40 isnt that steep of a price if you're buying a $400 iPhone?
Im in the UK. The thing is, my Dad works kinda high up at BT so I get my contract free. I wouldn't mind paying the iPhone contract if it was £20, but its nearly double that, and I don't think its worth it. Not only that, but I have no O2 signal where I live, so it would be kinda rubbish... I just wanna enjoy the iPhone!