Although T-Mobile is only the fourth-largest carrier in the U.S. in terms of subscribers, it seems to be setting the trend for all U.S. carriers when it comes to new features for customers.

Following in T-Mobile's footsteps with 'Data Stash', AT&T has unveiled its Mobile Share Value plan for all AT&T subscribers, allowing them to bring unused data over from last month. The plan allows AT&T customers to store up unused data and splash out the next month, making it optimal to save data one month before going on vacation.

Like Us on Facebook

There are a few caveats to AT&T's plan, including the fact users can only hold onto data for one month. On T-Mobile's plan, users can store data for a full year, making it more lucrative for the customer.

T-Mobile's CEO John Legere has already pitched in on the new AT&T plan: "We were the first to do this and still the only ones to get it right! 10GB to start your Data Stash, a year to roll over and NO OVERAGES!"

He followed up with a question on when Verizon Wireless and Sprint would bring their own Data Stash plan: So AT&T was the first ... with their knockoff of Data Stash... just waiting for VerizonWireless and Sprint to follow suit"

T-Mobile narrowly missed a third place finish in the U.S. carrier standings, losing to Sprint by a few thousands subscribers. However, T-Mobile managed to add over 10 million subscribers in 2014, much higher than Sprint and AT&T.

TagsAT&T, Data Stash, Mobile Share Value, T-Mobile, U.S. carriers