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AT&T has the second-best thing: SMS.
The funny thing is - they used to.
With iOS5, any iPhone owner who sends an SMS to another iPhone owner actually sends it through Apple, not over SMS! So suddenly the vast numbers of iPhones they are selling mean a dramatic drop in SMS revenue.
It makes you wonder if that's why the sudden squeeze in other areas, as they need to adjust for making less money from the same customer base.
That's the initial, default behavior in IOS5, but it's possible to disable that and send messages with normal SMS.