http://www.macrumors.com/2009/06/17/atandt-extends-iphone-3g-s-upgrade-pricing-to-many-customers/
AT&T's new policy:
"All of that said, we've been listening to our customers. And since many of our iPhone 3G customers are early adopters and literally weeks shy of being upgrade eligible due to iPhone 3G S launching 11 months after iPhone 3G, we're extending the window of upgrade eligibility for a limited time.
We're now pleased to offer our iPhone 3G customers who are upgrade eligible in July, August or September 2009 our best upgrade pricing, beginning Thursday, June 18."