T-Mobile US Inc. (TMUS) shares plummeted 5.09% in pre-market trading on Wednesday, following the release of its fourth-quarter financial results.

The wireless carrier reported quarterly earnings of $1.88 per share, falling short of the FactSet consensus estimate of $2.05. Revenue for the quarter was $24.33 billion, slightly above expectations.

The decline was driven by a miss on key customer metrics. T-Mobile added 962,000 net postpaid phone customers, below the 981,330 analysts had anticipated. Furthermore, the postpaid phone churn rate increased to 1.02% from 0.92% a year ago, indicating higher customer turnover amid intense competition from rivals like Verizon, which has been offering aggressive promotional deals.

The company's full-year adjusted free cash flow guidance of $18 billion to $18.7 billion also came in below the Visible Alpha estimate of $18.90 billion, likely impacted by integration costs related to its merger with UScellular.