We just learned that AT&T's policy of allowing current iPhone owners a subsidised upgrade—even though they're only at most one year into their two-year contracts—quite literally applies to current iPhone owners. That means that if you sold your iPhones recently in order to raise money for the new one, you might be out of luck. And by out of luck, we mean you have to pay the unsubsidised price (US$399 for 8GB and US$499 for 16GB) in order to upgrade to the iPhone 3G, not the US$199 and US$299 you thought you were going to pay. Let us explain.
We've confirmed from an AT&T rep that if you aren't using the iPhone, then by definition you aren't an iPhone customer. That makes you a regular AT&T customer with regular upgrade qualifications. How does AT&T know whether or not you're using the iPhone currently? Well, when you stick your old SIM into a new phone, they can detect exactly what you're using even if you haven't switched your plan to something else besides the iPhone plan. Bottom line is, you should go to AT&T and use their eligibility checker to see if you qualify. If you're really lucky, you only sold your phone recently and you haven't gotten around to sticking your SIM into something else.