Think of it this way, what good are the volumes when the network via which your products are being used is crammed? Besides, which company doesn't love selling more volumes than they currently are? In my viewpoint, Apple would like to introduce more carriers to tackle the on growing traffic on overburdened AT&T network, and that too in addition to AT&T, just because their contract with Apple will be coming to an end soon doesn't mean they will ditch AT&T at once, lots of legal and customer formalities need to be fulfilled in order to take that step, the transition is not that easy as it might sound.
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