Please read this new york times article. The article quotes AT&T head of consumer services as saying that the caps were "inevitable". Can apps that allow live video streaming gain traction if people started watching every single byte that went through the network?
Assuming they are able to come up with a reasonable pricing on the data meter, will it put downward pressure on voice tarriffs? Only time will tell. For an interesting article on cell phone pricing, please head over to this new york times article.