A few months ago, T-Mobile US Inc looked set to dominate a race for airwaves reserved for smaller, emerging players in an upcoming U.S. auction, a feat that would help it compete with U.S. wireless heavyweights Verizon Communications and AT&T Inc. In part of a low-frequency airwaves auction, which includes spectrum set aside for non-dominant carriers, No.3 U.S. wireless player T-Mobile was the only major bidder in sight. But new competitors for the spectrum are surfacing, which could dash T-Mobile's chances of acquiring enough spectrum at a price it can afford.