All true breakthroughs in an art form come when there is a change in perspective. Some say that Italian Renaissance painter Masaccio (1401-1428) "rediscovered" how to paint in perspective after the technique had been lost in the Dark Ages, and the Renaissance painters all used it after he showed the way. The cubists including Picasso, painted the "time" dimension and brought painting to a new height.
It is because of this notion of how a change in perspective can alter art or behavior that I think the dual camera on the iPhone 4G may change common communication. I remember being at the 1964 World's Fair in Flushing New York, the location used at the end of the Men in Black movie. It was there that I first saw AT&T's video phone -- which has been one of those great technologies that has always been just around the corner. So why do I think the iPhone 4G may unlock video phoning? Because it not only allows the user to show him or herself, but by to seamlessly change to show what they are seeing. This technologically advanced, shared voyeurism is a very sophisticated change in the point of view.
In addition, their integration with the phone call makes it effortless. You can easily begin with a voice call, then show something, and then go back to voice. There are not only many social settings in which such a powerful tool will be used, but many business settings from underwriting to designing.
In the famous phrase of Donald Norman who wrote The Psychology of Everyday Things in which he puts forth the idea of "affordance", saying that a device with good affordance is easy to use. It seems to me that the 4G has clear affordance for how people communicate and they have deftly spliced video into the experience. Maybe after 46 years, video conferencing on the phone, from person to person, will finally become real.