Beginning in January 2015, T-Mobile will start offering rollover data for Simple Choice customers who buy 3GB or more for smartphones and 1GB or more for tablets.

Dubbed Data Stash, the new program is kicking off by putting 10GB of free LTE data into each customers’ new reserve. Once that’s used up, subscribers’ unused high-speed data will start being banked in the Stash where it will expire after one year. Subscribers will automatically start dipping into the Stash once they exceed their monthly high-speed limits.

When asked why T-Mobile named the new program ‘Data Stash’ instead of just rollover data, CEO John Legere said, “Because it’s cooler.”

Expanding on the reasoning for the new Uncarrier move during a T-Mobile press conference Tuesday, Legere said Data Stash is an attempt to make it easier for people to experiment with using their data. He said hopefully over time users will get more comfortable using more data and that it will translate to ARPU growth for T-Mobile.

But some analysts were not as enthusiastic about the new service feature from T-Mobile.

Susan Welsh de Grimaldo, director of wireless operator strategies at Strategy Analytics, asked why T-Mobile won’t just offer cash back at the end of the month to subscribers who didn’t use their entire high-speed data allotment.

“T-Mobile should realize consumers do not need to roll over their data, they need to control it and have visibility and options to buy as they need it with real-time, on-device tools,” said de Grimaldo.

Lynnette Luna, principal analyst at Current Analysis Consumer Group, said that Data Stash isn’t a “huge differentiator” considering that T-Mobile has already done away with data overage charges. But she said the move does strengthen T-Mobile value carrier image.

“The Un-carrier 8.0 offer certainly plays on customer fears of using too much data and serves as another strong marketing salvo—especially during the critical holiday selling season – against AT&T and Verizon that rely on their customers buying bigger buckets of data to avoid overage fees,” said Luna.

The move could lead T-Mobile subscribers to see less use for ARPU-driving big data buckets.

Since T-Mobile subscribers need to buy at least 3GB plans for Data Stash to kick in it could cause 1GB subscribers to trade up. But it could also cause subscribers with more than 3GB to trade down, said Cowen & Co.‘s Colby Synesael, according to Barron’s. But he added that program would likely drive more customer adds and lower churn for T-Mobile.

The potential for increased customer retention has Citigroup’s Michael Rollins believing that other carriers like AT&T, which when it was still Cingular introduced a similar concept in rollover minutes

T-Mobile’s Data Stash is similar to what Tier 2 carrier C Spire Wireless newly announced plans that offer to rollover up to 6GB of LTE data from month to month.