Of course AT&T doesn't want to compete with T-Mobile. But unfortunately for them, that's exactly what's happening, and they will have to respond in some fashion unless they like losing customers to T-Mobile.
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That desperation
appears to be paying off.
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Unlimited data on T-Mobile isn't going away anytime soon. Customers on T-Mobile unlimited plans are paying more than those on the tiered plans, sometimes as much as $30 more. This is the exact opposite from AT&T and Verizon, who priced their unlimited tier very low compared to the tiered offerings, which motivated them to eliminate it.