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That is what many do. They start a line in iTunes then upgrade their device and are able to "grandfather" into the unlimited plan. AT&T, however, will automatically make it the $30.00 3G/LTE unlimited plan and not just the $20.00 2G (EDGE) plan.

So what's the difference besides price?
 
So what's the difference besides price?

The 2G (EDGE) unlimited plan is not supported on newer devices as it is not the appropriate data plan for them. Therefore, the AT&T system will automatically detect that a newer device is used or on order and "upgrade" the plan to an unlimited 3G/LTE plan under the grandfather clause.
 
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