According to Paul Roth, “exclusivity provides enormous consumer benefits and results in devices and innovations that would not otherwise be introduced.”
Honestly Mr. Roth, the innovations would carry on either way whether Apple decided to stick to one carrier or multiple, I think what you are refering to is it promotes AT&T a lot more than it does other carriers.
I personally believe, if Apple wants to unleash the true potential of its iPhone and its App store, it should stop cutting deals with only one service provider and just make the iPhone open to all carriers just like its SDK.
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