The first quarter saw more of the same mixed results in the U.S. wireless industry as handset upgrade rates reached an all-time low and subscriber growth slowed while profitability and margins topped records set just two quarters ago, UBS said in a research note.

"(T)he competitive intensity has eased (at least for now) with Sprint focused on cost cutting/profitability and T-Mobile seemingly content with its share of subscriber gross additions," according to UBS. "AT&T (NYSE: T) and Verizon (NYSE: VZ) have largely held the line on pricing and AT&T's willingness to shed postpaid phone subscribers has contributed to resilient trends at Verizon (its largest porting partner). Together, handset subscriber growth for AT&T and Verizon continues to slow."

The relatively "benign" competitiveness partially belies a mobile industry that has seen significant -- if not mind-blowing -- disruption over the last two years. T-Mobile (NYSE:TMUS) has demonstrated remarkable momentum with an uncarrier strategy that has seen it evolve from an also-ran to a legitimate threat to the two dominant players, overtaking Sprint to become the country's third-largest operator along the way. Sprint, meanwhile, is struggling desperately to regain solid financial footing as it scrambles to grow its customer base.

"The key question is whether AT&T will continue to accept postpaid phone losses," UBS said. "Management is focused on improving sub trends with new bundled offerings while attacking the low end of the market with its Cricket offering. We expect AT&T's aggressiveness to ramp in 2H with the expected launch of its new OTT products (creating the new digital bundle) and the next iPhone refresh."

And while the mobile waters may be fairly calm as we reach the mid-point of the year, competition may once again bubble up in the coming months. Not only will AT&T bring its DirecTV-branded video service to market, Verizon is sure to continue to pursue its expansion into media with Go90 -- and, perhaps, with the acquisition of Yahoo's Internet business. Meanwhile, Sprint (NYSE: S) appears to have secured the liquidity it needs to survive, at least for the foreseeable future.

Increased competition could result in slowing growth for T-Mobile, as Pacific Crest Securities predicted earlier this week. Pacific Crest noted that such a slowdown is somewhat expected, however, given T-Mobile's massive gains in recent quarters.

"Given its market status, competitive moves by AT&T have historically caused a domino effect across the industry, inciting responses from T-Mobile and Sprint, and perhaps most importantly, pulling Verizon into the fray," UBS analysts wrote. "While we believe the industry is set up for another few quarters of similar trends, including prolonged upgrade cycles and strong profitability, we think a potential storm is brewing as 4Q approaches."

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