John Legere teamed up with Yahoo!’s David Pogue this morning to reveal Un-carrier 8.0, which is officially known as Data Stash.

Data Stash is basically rollover data, letting you carry your unused 4G LTE data from one month into another. Data saved in your stash will be available for up to a year, and there’s no limit to the amount of megabytes that your Data Stash can hold. The offering will be available to all post-paid Simple Choice customers with a 3GB smartphone plan or 1GB tablet plan. That includes individuals, families and businesses.

T-Mobile’s Data Stash will launch in January 2015, and to celebrate its arrival, every customer that’s eligible for Data Stash will receive 10GB of 4G LTE data in their stash for free.

In addition to announcing Data Stash, T-Mobile today gave us an update on its 4G LTE network progress. T-Mo says that its LTE footprint now covers 260 million Americans and that its Wideband LTE service is available in 121 metro areas.

T-Mobile also recently deployed its 700MHz service in Cleveland, Colorado Springs, Minneapolis and Washington D.C. to boost in-building coverage in those areas. Looking ahead, T-Mo plans to reach 300 million people with its LTE coverage in 2015. So there’s T-Mobile’s latest Un-carrier move.

Now that it’s official, what do you think?

Source: T-Mobile