T-Mobile US exceeded Wall Street’s quarterly estimates but offered a full-year earnings forecast that may be light amid a costly federal auction of airwaves for new 5G spectrum. The No. 2 wireless carrier continues to generate faster customer growth than rivals Verizon Communications and AT&T.

Fourth-quarter earnings totaled 60 cents a share, the Bellevue-based wireless company said Thursday, exceeding the average 52 cents that analysts were forecasting. Revenue grew to $20.3 billion, exceeding projections of $19.7 billion. Adjusted earnings before certain items this year will range from $26.5 billion to $27 billion, slightly below some estimates.

T-Mobile is constrained by federal auction rules from issuing comments about its bidding and doesn’t expect to say more until a March investor meeting. New subscribers this year are forecast to total 4 million to 4.7 million after the company signed up a record 5.5 million in 2020, including 2.2 million phone customers. The latter tend to be more loyal and lucrative than hot spot and tablet users.

The company achieved savings of $1.3 billion from its takeover of Sprint in the form of revenue gains and reduced costs from combining the companies. T-Mobile also plans to say more about its integration efforts next month.

The second-largest U.S. wireless carrier borrowed $3 billion to help cover bids in a record $80.9 billion federal airwaves auction. T-Mobile already has a wide lead in ownership of midband 5G spectrum and is hoping to maximize that advantage against its phone and cable rivals that are also bidding.

T-Mobile says it now offers “ultra” 5G midband service — which can deliver wireless speeds comparable to home broadband — in 1,000 cities and expects to double coverage by the end of 2021.

T-Mobile fell as much as 3.2% to $126.44 in extended trading Thursday. The stock gained 72% last year, compared with a 16% advance for the S&P 500 index.