Continuing a theme that persisted throughout 2014, where T-Mobile blazes a path, the bigger wireless carriers follow, and more consumers benefit. This time around, the innovation is rollover data, a plan by which customers of the carriers can move unused data bandwidth to the next month.

T-Mobile announced its rollover data plans in mid-December, capping off a year in which the nation's smallest of the big wireless carriers has moved to completely upend the ways in which these companies do business and interact with their customers.

"If you buy data, it's yours. Roll it over," T-Mobile CEO John Legere said during a live online interview in December. "Everybody, come and get it. Especially if you're with the bad guys [rival carriers like AT&T and Verizon]. We're waiting for you."

In T-Mobile's case, however, the rollover data is a one-year offer and is aimed very clearly at gaining new customers from rivals. The aggressive firm's tactics have worked, too: T-Mobile—which bills itself as the "uncarrier"—says it picked up an additional 8.3 million new customer in 2014, and 2.1 million new customers in the fourth quarter of 2014 alone. "2014 was a record breaking year," Legere says.

Now AT&T says it, too, will add data rollover, in this case to its Mobile Share Value programs for both new and existing customers. But AT&T Mobility president CEO Ralph de la Vega bristles at the notion that his firm is copying the competition.

"It's just the opposite," he claimed at CES this week in Las Vegas, noting that AT&T long offered voice minute rollover. (AT&T plans now offer unlimited voice calling, however, like the rest of the industry.) "I think [T-Mobile] took our rollover concept and we're flattered that they decided to use it for data. We had plans to roll it out here at CES for a long time. We trademarked the name 'Rollover Data' earlier in the year."

Which year is unclear, but no matter: For now at least, customers on both AT&T and T-Mobile can benefit from having their unused data bandwidth rolled forward to the next month. AT&T's is more restrictive in that you only get month-to-month rollover with no aggregation over many months. But T-Mobile's plan is limited to the next year alone. (Though that can change.) On the flipside, T-Mobile is also offering its users a 10 GB pool of data they can carry forward throughout that next year.

Now the only question is when Verizon Wireless follows suit. If history is any guide, they will do so, and soon.