The battle between T-Mobile and its competitors is getting intense. T-Mobile’s challenges, including its latest “Uncarrier 4.0” initiative and its CEO’s guerilla PR tactics at an AT&T conference, both at CES, have reasons for its competitors to concern. The assaults that T-Mobile has launched since mid-2013 appear working—T-Mobile reported 4.4 million net subscriber gains for the year 2013, the largest among its peers.

Its competitors’ responses have been swift, too. Each of the top three carriers has launched a device upgrade program to counter T-Mobile’s, lowered bills for people bringing their own devices, and AT&T even launched a similar “buyout” program as T-Mobile’s, one week before the latter’s CES announcement, to head off the impact.

T-Mobile’s “Uncarrier” moves and its competitors’ counterattacks make the year 2013 the most exciting one to watch for us as industry observers. For years, the wireless service industry has been the “build” and “consolidation” stories—new-generation network build-out and marketing pitches about who has the fastest network, then both successful and failed mergers and asset swaps. Meanwhile, consumers got slowly increasing wireless bills as they upgraded their phones and supersized their data plans. In a fast expanding mobile data market, dazzling new smartphones and fast data speed seemed working for carriers to upgrade basic phone users to new data plan users. Customer loyalty seems a second thought as carriers are protected by contracts and consumers have limited choices due to carrier consolidations in recent years.

But the year 2014 looks like a “loyalty” story for the industry, thanks to T-Mobile’s moves. With all the incentives and perks that T-Mobile has assembled—such as lowered data plan rates, free international roaming, easy ways to upgrade phones, and the offer to pay for contract penalties for customers switching to T-Mobile--it will be a true test of mobile customers’ loyalty throughout the industry.

Parks Associates’ consumer data showed that almost 50% of mobile phone service customers did not change providers over the last 10 years, a quarter switched once, and only 13% switched three times or more. In other words, it has been a relatively very stable environment, thanks to the standard two-year contract into which customers are locked. Breaking down the stats by carrier brand, Verizon and AT&T have the most stable customer base: 62% of Verizon and 56% of AT&T customers have been with them for more than 5-years.

In our latest consumer research analyzing the life time value of customers, AT&T stands to lose the most if it lets its most valuable customers defect. About 35% of its customers are worth $5,000 or more, the highest among the big four and compared to 21% for T-Mobile. And AT&T should be a bit more concerned—our data also shows that 18% of AT&T customers are considering switching in the next 12 months, the second highest among the big four. But AT&T also has a fighting chance—it has the highest % of customers wanting to upgrade their services among the big four.

How the competition will play out in 2014 is of our focus. Carriers will pull all the tricks to stop subscriber losses and steal the most valuable customers with sweetened offers from competitors. The U.S. wireless industry has entered a new era in which fast data ARPU growth is no more, and customer loyalty becomes the fighting chance for thriving in an intensely competitive market.