Fortune reports that AT&T is preparing to offer a $200 subsidy for buyers of the next-generation iPhone, widely expected to be introduced this summer. It writes that since the new, presumably faster models will start at the same $399 base price as the current iPhones, that will drop the effective price to $199.

I certainly assume that Apple and AT&T are working hard to get the iPhone to a price that puts it within reach of the most people. Fortune writes that AT&T has found that iPhone owners spend twice as much as the average customer because they buy data plans. (This is consistent with what AT&T said to investors on its earnings conference call last week.)

But as reported, there are some bits of the story that don’t make sense. Fortune wrote that AT&T will offer the subsidy to people who buy the phones in its stores, but not to those who buy in Apple stores. I can’t imagine that Apple would want to sell iPhones for even a dime more in its stores than in another store. (Apple keeps exceedingly tight control over its pricing.)

And there is no underlying economic reason for AT&T to offer anyone an incentive to buy the iPhone in its stores. No matter where you buy your iPhone, the only way to use it legitimately is on the AT&T network, which requires a two-year contract. What’s more, Apple has a much greater incentive to get people into its stores — where it can try to sell them Macs — than does AT&T — which has little more to offer than the odd headset and case.

My guess is that this report may be pointing the way to one of two (not mutually exclusive) developments:

AT&T wants to lower the price of the phone and raise the price of the data plans. Right now the unlimited data plan for the iPhone costs $20 a month, far less than the $45 a month the company charges for unlimited data on a BlackBerry. Now that the iPhone can also connect to corporate e-mail networks, AT&T may not be able to justify a gap in the monthly fees for its smartphones. To make up the difference, it could raise data rates and subsidize the phones. My guess, however, is that the $200 subsidy would be available to people who buy the phones from Apple stores as well.

Apple will start selling unlocked phones. Apple has found that an enormous number of its customers are unlocking the phones, using third-party software, to use on carriers of their choice. If Apple were to remain in keeping with its culture, it would simply try to make the next-generation iPhone even harder to unlock. But then again, it could decide to avoid this fight, change its business model and just sell phones. That would mean, presumably, giving up the monthly fee it gets from AT&T and other carriers. In this scenario, Apple might well raise the price of the iPhone to, say $599. But then it would have carriers offer subsidies in return for contracts, as most other handset makers do.

Here’s one prediction I will stand by: We will have more leaks that don’t entirely make sense and are not consistent with each other until Steve Jobs ascends some stage somewhere with some answers.