Hi. I purchased my iPhone 4 through AT&T online. I love it, but I regret not getting the 32GB model. I'm still within the return window. I'm wondering if I could just go to my local At&t store and simply pay the difference? Anyone have any experience with this? Will I have to mail it back, or if I bring to a local store will I have to wait while the funds are credited back to me? I did an early upgrade, so the phone cost me $399.99 before tax. If I can just pay the $100 difference (maybe plus restocking fee) I'd definitely go for it; but if I have to wait for the original $400 to clear again I'll just say forget. Sorry for the long winded explaination