U.S. Cellular’s unlimited-data plans have helped drive data usage up more than 50% over last year, according to Wells Fargo Securities.

The Chicago-based network operator earlier this week posted 44,000 postpaid smartphone net additions in its more recent quarter, losing 15,000 net feature-phone users but gaining 6,000 net connected devices. Postpaid churn came in at 1.16%.

Shares jumped roughly 3.5% following the earnings release, indicating investors were pleased with U.S. Cellular’s quarterly results. And Jennifer Fritzsche of Wells Fargo credited much of that success to the unlimited plan the carrier launched in February.

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“U.S. Cellular ended the quarter with 1.7 million subscribers—39% of its postpaid base—on its Total plans,” Fritzsche wrote in a note to investors. “Of its Total plan base, 31% of customers are on an unlimited plan. U.S. Cellular’s total data usage has grown 51% on a year-over-year basis and was up 14% sequentially, with average handset data usage of 3.1 GB per month. Customers (on) unlimited plans use nearly three times its average customer data usage.”

Whether U.S. Cellular can continue to thrive in a market where nearly every service provider offers unlimited data plans is unclear, however, Fritzsche noted. Unlimited plans clearly drive up data consumption in a major way, which increases traffic on wireless networks—which will likely require operators to invest more heavily in their networks eventually. And that could tilt the market in favor of larger carriers with deeper pockets.

“U.S. Cellular in particular has seen strong penetration with its unlimited plans, with over 500,000 customers currently on those data plans,” Fritzsche wrote. “We think it will continue to be difficult for U.S. Cellular to consistently grow service revenues, as price competition shows no signs of abating. With Sprint and T-Mobile continuing to operate as separate entities, we would expect pricing pressures to only pick up around the iPhone cycle in Q4 2017 and Q1 2018. Furthermore, the ongoing geographic expansion of T-Mobile likely will also create more competitive pressures in certain U.S. Cellular core markets.”

Fritzsche maintained Wells Fargo’s “market perform” guidance for U.S. Cellular but lowered its target price to $35 from $39 per share. The stock was trading at $33.85 as the market closed Thursday, up 2.7% on the day.