I've heard off rollover minutes but rollover data? That's actually a pretty good idea.
T-Mobile today announced its next industry-rocking Un-carrier™ move − eliminating the infuriating wireless industry practice of confiscating unused data you’ve already paid for. With Un-carrier 8.0, high-speed data you don’t use each month automatically rolls into a personal Data Stash™ so you can use it when you need it for up to a year. And, the best part is that Data Stash is included at no extra charge for every single new and existing T-Mobile customer – individual, family or business – on an eligible postpaid Simple Choice plan who buys extra high-speed data for their smartphone or tablet.