Remember the days when we waited till 7pm to start calling our friends? Or the days of being careful who to call because they weren't with the same phone provider you were? Or constantly keep track of how many minutes we had left before the bill cycle ended? You get the point. Today we're still worrying about the same thing but with data. T-Mobile has introduced a new concept of data rolling over and it's called the Un-Carrier Data Stash. Data Stash lets you save your unused data and re-use it at a later time when you do need it.