As it turns out, there was a misinterpretation with the parts numbers that Apple sent to retail stores. The part numbers actually correspond to unlocked iPhone 4s, not new MacBook Airs. Apple has sold unlocked iPhone 4s internationally but never in the U.S. Unlocked mobile phones are simply less in demand in the U.S. due to the fragmentation in service amongst U.S. carriers.
"Unlocked" simply means that a mobile phone is not tied to any particular carrier. In Europe, customers can buy an Unlocked phone and easily switch between carriers by simply replacing the SIM card. In the U.S., users could theoretically switch between AT&T and T-Mobile in this manner for voice calls, but 3G service is not compatible between the two carriers. This is what makes the sale of unlocked iPhone 4s in the U.S. so strange.
But the word we've received is that they've shipped to Apple Stores this week and that they will be priced at $649 and $749 for 16GB and 32GBs, respectively. The higher price reflects the lack of long term contract that normally accompanies a mobile phone purchase as well as the unlocking.