In the smartphone world, things can change a lot within a short span of time. As a result, those of you who have to have the latest and greatest thing in your pocket might be inclined to keep buying phones and, consequently, take losses on them when you sell them. T-Mobile's JUMP! On Demand plan previously allowed phone junkies to switch devices three times a year, but the policy has now been changed to once every 30 days.

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