Analysts at global investment banking firm Jefferies have raised concerns over AT&T and Verizon Wireless' lack of "rational" pricing in 2014, which has allowed T-Mobile and Sprint to win over new customers in the U.S.

T-Mobile completed its best year in 2014, adding close to 9 million new subscribers, more than Verizon Wireless. The main reason for T-Mobile's success is the adoption of 'Un-Carrier' plans, allowing simple customer subscriptions to get added bonuses, alongside cheaper monthly payments.

Like Us on Facebook

T-Mobile's CEO John Legere has also become a public face everyone seems to like, while AT&T CEO Randall Stephenson and Verizon Wireless CEO Daniel Mead are less visible and don't speak to the people like Legere.

Creating a likeable brand will allow T-Mobile to maintain strong sales going into 2015, especially if it is able to promote all of the past Un-Carrier announcements, and continue offering better deals.

Sprint is also on the rise, adding 1 million new subscribers this quarter. The company is reforming the way it does business, and is looking to start price wars against all three U.S. carriers.

The issue for Sprint is past reviews show shoddy customer service and lackluster wireless service outside of a few key areas. Even though the latter also affects T-Mobile, John Legere has confirmed T-Mobile is buying more spectrum to cover the issues, while Sprint has not given any such guarantee.

Sprint CEO Marcelo Claure does not have the public identity John Legere has managed to carry forward through 2014, but Claure founded Brightstar Corp and has raised the wireless distribution service to a company making $10 billion in gross revenue, showing he has the capabilities to reform a company.

Verizon Wireless and AT&T still hold the lion share of subscribers, over twice as many as T-Mobile or Sprint. The two tier 1 carriers also hold the most wireless spectrum, but in 2015 they need to compete heavily against T-Mobile and Sprint, before the third and fourth place carriers start making real leaps in the wireless industry.

TagsAT&T, T-Mobile, Sprint, Verizon wireless, U.S. carriers