The way they have things set up, it's going to be hard for them to keep their generous deal with AT&T intact while opening the iPhone up to other carriers. The second the iPhone is available elsewhere, Apple loses a lot of the leverage that got AT&T to pay the iPhone's huge subsidy.

You can bet that if Apple could negotiate terms with a second carrier that would increase their profits, they would be all over that. I suspect they're having a hard time finding a generous enough offer to compensate for a weakened deal with AT&T.