T-Mobile’s customers are the most loyal of any major wireless carrier in the country, according to Business Insider.

BI Intelligence’s Digital Telecom Consumer survey found that 23% of T-Mobile’s subscribers said they wouldn’t switch carriers “for anything,” topping the 16% of AT&T customers and 15% of Verizon customers who said the same. Sprint finished a very distant fourth in the survey, with only 7% of subscribers saying they wouldn’t switch service providers.

As BI Intelligence points out, T-Mobile’s advantage in customer loyalty is especially noteworthy considering the saturated smartphone market in the United States. Roughly 77% of consumers own a smartphone, according to Pew Research, which has resulted in an ultracompetitive market that has seen every major operator launch unlimited data services in the last year.

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“Average revenue per user across the Big Four dropped to $45 in Q1 2017, from $49 in Q1 2014,” Business Insider wrote. “To remain profitable, carriers need to maintain or grow their customer base.”

Meanwhile, the industry-wide move away from two-year service contracts has made it easier for users to switch carriers.

It isn’t clear that T-Mobile’s advantage in customer loyalty is paying real dividends, however. The carrier reported a record low branded postpaid phone churn of 1.1% in the latest quarter, down 17 bps year over year, but every major U.S. operator enjoyed low churn during the relatively placid quarter. And T-Mobile’s blended average monthly churn during the quarter was 2.24%, barely outpacing Sprint (2.28%) and significantly trailing AT&T (1.28%) and Verizon (1.19%).

And like its rivals, T-Mobile’s coverage and capacity are vulnerabilities in a highly competitive market. Business Insider reported that 42% of T-Mobile’s customers said they’d switch to a provider that offered better coverage where they live, while smaller percentages of AT&T and Verizon customers said the same.