An unlocked iPhone in the US?

The Apple buzz machine is starting to get going for the June launch of the 3G iPhone. Be ready to hear any possible rumor, from GPS support, an iPhone with a keyboard, a Mini iPhone, a Large iPhone (a laptop real replacement). Until Jobs shows up on stage, it will be just rumors.

One very interesting came up yesterday on Fortune. In a nutshell:

When the 3G iPhone is introduced this summer, AT&T, the exclusive U.S. iPhone sales partner with Apple, will cut the price by as much as $200, according to a person familiar with the strategy.

AT&T is preparing to subsidize $200 of the cost of a new iPhone, bringing the price down to $199 for customers who sign two-year contracts, the source says. Apple is expected to have two versions of the new iPhone, an 8-gigabyte-memory and a 16-gigabyte-memory model with price tags widely expected to be $399 and $499.

I have seen many reactions to this story, mostly linked to the low price of the device and the fact this will make sales explode for Apple.

One thing I haven't read (yet) but I feel it is the real story: if at&t subsidizes the phone to $199, why would I buy a $399 phone at the Apple Store? One and only reason: because it would be unlocked... A phone you can use with Tmobile and overseas.

It is not impossible, since Apple is doing it in Europe already (although the price of the unlocked phone is way higher than $399), but it is very strange. Everywhere we read that at&t had a lock (pun intended) on the iPhone in the US for five years. The story above calls at&t "the exclusive U.S. iPhone sales partner with Apple". If Apple comes up with an unlocked phone in the US after one year, than the lock was unlocked pretty fast. How exclusive is that?