As the end of the third quarter nears, T-Mobile and Sprint appear to be maintaining their subscriber momentum, while Verizon and AT&T are in worse shape than previously thought.

That's the conclusion of UBS Global Research, which on Wednesday issued its revised estimates of third-quarter wireless financials.

UBS now expects T-Mobile to add 820,000 net postpaid phone subscribers in the quarter, a 120,000 boost over its previous estimate of 700,000. And it forecast Sprint to gain 235,000 subscribers, a slight boost over the previous 219,000 estimate.

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Meanwhile, Verizon's forecast is far dimmer than expected: Just 92,000 net adds, down from the previous estimate of 360,000. AT&T will lose more subscribers than originally thought as well: 230,000 net losses instead of 190,000.

Partially driving these changes are the “competitive intensity” of the free iPhone 7 promotions, which T-Mobile and AT&T ended on Sunday but Verizon and Sprint are still offering. “We are updating our wireless estimates to reflect stronger 2H upgrade activity and lower equipment revenues due to competitive trade-in offers,” UBS analysts wrote in the forecast.

Even though Verizon's promo is still ongoing, UBS said the carrier is still suffering from too-low churn. “We estimate postpaid churn remains low for Verizon but gross adds slowed given competition, leading to lower overall net adds.”

Meanwhile, the analysts noted that T-Mobile replaced its promo with other attractive offers, and thus they didn't expect the carrier's otherwise strong subscriber growth to be affected.

In addition to the subscriber changes, the forecast also expected the promotions to affect the carrier's profit margin expansions – since they mean the carrier is paying significantly more per user device than otherwise.

Interestingly, however, the forecast estimated the same revenue impact to all four carriers from the promotions, not taking into account recent reports that Sprint's promotion is more profitable than expected. Thus, it's possible Sprint's revenue will take less of a hit than the forecast.

As a result of the financial update, UBS gave T-Mobile US its top pick for investors, while it rated AT&T, Verizon and Sprint as neutral.

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T-Mobile posts 890K net postpaid subscriber adds, 1.9M total net adds