T-Mobile John Legere announced at Un-Carrier 8.0 another new incentive to switch carriers named Data Stash.

Customers on T-Mobile's Simple Choice package using over 3GB (or 1GB on tablet) will be viable for the new program, allowing unused data from one month to be moved to the next. Users will be able to store unlimited amounts of data in the stash and keep it there for 12 months, before it is wiped from T-Mobile's records.

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To kick off the new program, T-Mobile will add 10GB to all customers viable for the new program. The stash will be available to check on the T-Mobile app. The 4G LTE customers will be the only users who get the deal. T-Mobile wants to make it easy to save up data, just in case the customer goes overboard one month on their regular data plan.

Other U.S. carriers have rollover plans, but T-Mobile is the first to implement it for 4G LTE users. The data stash also has no known drawbacks like Verizon and MVNO's options.

T-Mobile already does a lot more than the other three U.S. carriers for customers. The carrier has the lowest monthly payment rate out of the four, it offers more transparency with contracts and offers free incentives like music streaming to keep users happy.

In the past year, T-Mobile has added over 5 million new subscribers to the service. Compared to 2012 and 2013, this is a huge rise in popularity for T-Mobile, spurred on by CEO John Legere.

TagsT-Mobile, Data Stash, John Legere, mobile contracts, U.S. carriers