Why AT&T has a Lock on the iPhone

When AT&T mishandled public relations around the iPhone for the Nth time recently - in having no formulated or ostensibly correct answer about upgrade fees for existing subscribers - I heard plenty of folks counting the days until AT&T was no longer the exclusive U.S. carrier for Apple's iPhone.

I don't want to say that it ain't gonna happen, because we all know that where there's a business will, there's a technology way. But there are a few big bars in the way.