I purchased on 7/11 and am now considering changing from 16GB to 8GB. Does anyone know whether I can simply buy an 8GB from AT&T for $199 (assuming I would need to commit to 2 years from date of purchase) even as an established customer? If I do this and I sell by 16GB on eBay would the buyer be able to activate a used iPhone 3G? Any other suggestions for how I can make this switch?