AT&T has revealed details regarding its pricing policy for the iPhone 3G in the United States. As previously announced, the 8GB model will cost $199 and the 16GB model will sell for $299, and will be available at those prices to customers who bought the iPhone before July 11, who are activating a new line with AT&T and/or who are eligible for an upgrade discount. For customers who aren’t eligible for the upgrade discount and who…