one of a couple options really. since they can't just shut off wimax without getting their heads BLOWN OFF by angry customers who bought wimax phones, they would either have to offer exchanges for lte capable phones or keep the wimax on for a while.
where they run into a problem is in areas (like mine) where we dont yet have 4g and, if they never turn it on but do turn on lte...that is going to be an issue if they dont offer an exchange since all of these customers will have bought these phones thinking "i may not have 4g now...but ill have it soon!" and then, they get the news that it isnt coming and that their phones will never get use out of one of the features they "bought it for" and the sales people "promised" them.
i only make these points because i'm a sprint sales rep and i know for a fact that my local customer base will come in, screaming and yelling, that their phones arent getting the technology they were promised and my co-workers and i (along with the sales reps in similar areas) are going to have to deal with a lot of angry people