The sudden rush to offer unlimited data plans is taking a significant toll on all four of the nation’s major wireless operators, according to Cowen and Company Equity Research.

Both T-Mobile and Sprint trotted out unlimited data plans last August, and the carriers have sweetened their offers since the competition heated up. Meanwhile, Verizon launched an unlimited plan in February, reversing its long-held opposition to the model, and AT&T made its unlimited offering available to all customers—not just those with DirecTV subscriptions.

The unlimited craze has been a boon for data-hungry consumers, but is already proving costly for the carriers, Cowen said.

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“The first quarter of unlimited for all four carriers left much to be desired,” Colby Synesael of Cowen wrote in a research note this morning. “Both AT&T and Verizon incurred postpaid losses for the first time on record, a trend that could continue. Verizon specifically had its worst quarter in recent memory with a lackluster performance on nearly all sub metrics. Even T-Mobile’s guidance included a ‘less great’ postpaid net add increase of just +250,000. Combined with continued pricing pressure, AT&T and Verizon are pivoting to new avenues of growth such as Mexico, content, media, IoT and 5G, all of which can’t come soon enough.”

Mike McCormack of Jefferies echoed those thoughts, predicting the unlimited model will continue to make it more difficult for operators to monetize subscribers at least for the short term, even as data consumption continues to ramp up.

“The resurgence of unlimited plans is likely to delay more meaningful ARPU stabilization for multiple quarters due to the loss of overages and plan rightsizing,” McCormack wrote in a note to investors. “Impacts to ARPU on an incremental basis (i.e. for new subscribers) will depend on the number of accompanying lines activated. Our analysis suggests a willingness to use price with the hopes that multiline subscribers will churn less frequently. The move to unlimited also diminishes the ability to monetize growing data usage, removing an important lever of growth.”

The U.S. wireless market may grow even more competitive over the next year as cable companies and perhaps other newcomers try to elbow their way in to an already crowded space. If carriers continue to embrace the unlimited model, the ability to deliver ever-increasing amounts of data to customers could become a huge differentiator, Synesael observed.

“All four carriers believe they have plenty of capacity to handle the unlimited era,” he wrote. “Verizon seems more constrained with low MHz and high connections per tower. AT&T seems best positioned, which will only get better when its ~60 MHz are deployed (and largely subsidized by FirstNet). Sprint still seems questionable (lacking low/mid band, little capex per connection), but has more capacity per tower while also touting innovative technologies such as the ‘Magic Box’ where performance still remains to be seen.”