Why are you reading this article? If you’re the proud owner of an iPhone 4S or an iPhone 4 (old-school), you owe it to yourself to chug on down to Best Buy — today! — and take advantage of the company’s one-day-only trade-in promotion for an iPhone 5.

And did we mention that said iPhone 5 is free?

Here’s the deal: If you have a working iPhone 4 or 4S, Best Buy will offer up a $150 trade-in credit on the spot for the device. Ignoring sales tax and carrier activation fees – and, no, you won’t be able to sneak in an upgrade before your carrier-approved window hits – that essentially makes the 16-gigabyte version of the iPhone 5 completely free.

Of course, you’ll have to activate your phone and sign up for a two-year contract with Verizon, AT&T, or Sprint in order to reap the benefits of the free iPhone. And, no, you can’t be lazy about this one – you’ll have to get up out of your chair and trudge on down to a Best Buy retail store, as the deal doesn’t work online in any capacity.

If you’re one of the unlucky shoppers trying to make use of the deal in approximately 360 Best Buy stores or so with a special loophole attached to the trade-in program, you might be just plain out of luck. According to a report from TheStreet’s Laurie Kulikowski(Opens in a new window), a small number of Best Buy stores are a bit more tightly bound by municipal laws that restrict the stores’ ability to offer up an ideal trade-in situation, as a result of the promotion crossing over into what they would otherwise consider to be “pawn store” territory.

If you attempt to trade your iPhone 4 or 4S in at one of these stores, you’ll be asked to show your original receipt for the purchase. And if that wasn’t annoying enough, the receipt itself has to be from a Best Buy, which means that you’re going to be slightly hampered if you originally purchased your smartphone from, say, store dot Apple dot com.

On the plus side, Kulikowski reports that employees at Best Buy retail stores affected by this issue have been instructed to tell eager customers the location of the nearest Best Buy that isn’t bound by such a provision.

“We greatly apologize to our customers and assure them that there are alternative stores in those areas where they can take advantage of the promotion,” said Best Buy representatives in a statement.