iPhone isnt the problem here, it is using less data then AT&T anticipated ( AT&T CTO reveals iPhone 3G data usage lower than expected (Updated) ). AT&T's reluctance to invest in their network led to insufficient capacity and poor stability. IIRC they completely paused 3g investments for the entire year while transforming from Cingular to AT&T. You cant penny pinch like that and expect to roll out a quality network.