An analysis of Apple and AT&T's sales numbers reveals that the companies cannot account for more than 1 in 4 iPhones sold last year.

Of 1.45 million missing iPhones, it is believed AT&T is holding about 480,000 in inventory, leaving 27 percent of these iPhones with no official home. That's a little more than a million of the 4 million iPhones Apple shipped in 2007.

Those iPhones were likely unlocked to work on carrier networks other than those of Apple's operator- partners. 27 percent is also a far greater percentage of unlocked iPhones than the 20 percent some analysts expected.

And since Apple gets a (unknown) percentage of the monthly service fees its carrier-partners receive for each iPhone sold, the more iPhones that are unlocked the greater Apple's bottom-line is negatively affected.

For example, Apple has often stated it would like to ship 10 million iPhones in 2008. Should 30 percent of these be unlocked, resulting in no ongoing revenue for Apple from them, then Apple would miss out on $500 million of expected revenue, according to one analyst.

So why is the unlocked iPhone market so big? Demand.

When Apple released the iPhone last June you could only use it on AT&T's wireless network, which remains true for the U.S. So, from the beginning, there have been those who've made it their mission to unlock the iPhone so it could be used with operators other than Apple’s carrier partners, both here and abroad.

Even though there is an official way for some customers to unlock their iPhones in Europe now, by far the majority of iPhone unlocks are performed unofficially: Either one at a time by individuals for personal user or, of greater concern for Apple, in large quantities for shipment overseas—mostly to markets (all of Asia, for instance) where the iPhone isn't available yet.

[Via internetnews.com]