So an AT&T customer shows up at an AT&T Store with a first-generation iPhone and a hand-me-down iPhone 3G—a common enough scenario this week given that quite a few people are giving up their 3G units for the iPhone 3GS. “I’d like to upgrade the old iPhone to the new one,” the customer says, handing over two phones. “Sure,” says AT&T, “we can do that. But you’ll have to sign a brand new two-year…
