Any and every rumor is in the air about the iPhone these days, but this one is probably the first of the recent batch that sounds pretty interesting. The mobile phone market is a pretty tough customer - carriers need to lock their customers down, and there are plenty of handset makers who already have large stakes in their turf. Apple has already stepped up to bat - twice - by trying to partner with one of those handset makers, and I think it'd be difficult to argue that they got anywhere past even first base.
Considering Apple's strengths - making great hardware and software - in light of their past failures in working with Motorola in this space, it seems entirely plausible for the company to aim for the stands on their third time at bat. By both developing and - this is the key - selling the iPhone all on their own, Apple not only gets to design everything their way, but they get to sell it to a much broader audience by offering it as an unlocked device through their own retail stores, rather than as a subsidized tool to force customers to either sign or break contracts, depending on their circumstances. This means Apple gets to flex their engineering muscles and rake 100% of their own profits - not a bad prospect for a company who is used to working solo in the hardware department, and by now is probably feeling the heat from sexy music handsets like Verizon's Chocolate.
For now, however, this is simply my attempt at applying some logic to a rumor. It sounds possible, but only January's Macworld (or 'the first half of next year') can provide anything to bank on.