Strong T-Mobile sales and Verizon’s exclusive grip on Google’s Pixel are eating into Sprint’s postpaid phone sales, BTIG Research said this morning.

Walter Piecyk lowered BTIG’s estimates for postpaid net phone additions for both the current quarter and the first quarter of next year, citing both higher churn and fewer gross adds than expected. Fourth-quarter net additions were cut by 40%, to 372,000 from 638,000, while BTIG cut its estimate of growth of gross additions in the current quarter to 1.7%, down dramatically from 15.2%.

“This is a material slowdown in gross add growth from 18.7% in CQ3 (the third calendar quarter),” Piecyk wrote in a brief research note to investors this morning (PDF, reg. req’d). “Growth in gross adds had been accelerating for the past three quarters on the back of the 50% off rate-plan promotion and the ex-Verizon pitch-man marketing.”

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Indeed, Sprint introduced its half-off plans two years ago in an aggressive move to poach market share from Verizon and AT&T. The strategy has been successful, although it appears to be weighing on the carrier’s bottom line: In the third quarter, for instance, Sprint added 173,000 net postpaid phone adds, marking its fifth consecutive quarter of positive movement in that metric. But it lost $142 million during the period as both ARPU and wireless service revenues declined year over year.

“We also cut CQ1 2017 postpaid phone net add estimate to 102,000 from 166,000 based on cutting our estimate of gross addition growth in that quarter to 5.6% from 11.9%,” Piecyk continued. “We do not expect Sprint to extend the 50% rate plan to customers that are facing the expiration of this popular promotion that began two years ago. That could provide a headwind to Q1 churn.”

Sprint CEO Marcelo Claure said a few months ago that while the carrier is likely to drop the 50% off promotion after the holidays, the company’s new $60-a-month “unlimited data” plan had gained traction with customers who simply want more data than their current plans allow. And that could offset any potential losses from killing the promotion offering, he suggested.

“A lot of the customers who come, they don’t want 50% off, they want to pay what they’re already paying but they want to be able to get double or two and a half times (as much) data” than they currently use, Claure said in September. “That obviously helps in terms of bringing customers” with higher ARPU than those who take the half-price deal.

BTIG predicted its lowered forecast for Sprint will likely negatively the firm’s 2018 cash EBITDA estimate by $90 billion, but Piecyk didn’t lower its $2.50 price target for Sprint’s stock. Shares of Sprint were trading at $8.38 as the market opened this morning.