Ahead of John Legere stepping down as CEO in a few months, T-Mobile (NASDAQ:TMUS) has hit a new milestone. This week, the Un-carrier announced preliminary customer metrics for the fourth quarter and full-year 2019. T-Mobile reported 1.9 million total net additions in Q4, including 1 million branded postpaid phone net additions. Branded postpaid phone customers are the most valuable customers.

For the full-year 2019, T-Mobile posted 7 million total net additions, including 3.1 million branded postpaid phone net additions. That brings the company's total customer base to a whopping 86 million -- impressive growth compared to the 33 million customers that T-Mobile had at the end of 2012, when Legere took over.

T-Mobile executives sitting behind a table with microphones on the Q3 2019 earnings call

Image source: T-Mobile.

Maintaining its streak

T-Mobile notes that 2019 marked its sixth consecutive year of gaining over 5 million net customers and its 27th quarter in a row of adding more than 1 million net customers. Branded postpaid phone churn ticked up to 1.01%, up 12 basis points sequentially; churn commonly spikes in the fourth quarter thanks to new phone releases and carriers ramping up promotional activity in an effort to poach customers from each other. Branded postpaid phone churn was 0.99% in Q4 2018.

On the prepaid front, T-Mobile added 77,000 of those customers on a net basis in the fourth quarter and 339,000 in 2019. T-Mobile is already the No. 1 carrier in the prepaid market, which is why the company has agreed to divest Sprint's (NYSE:S) prepaid segment if their merger deal is approved.

"T-Mobile delivered another incredible fourth quarter with strong customer growth, despite a very competitive environment -- and we did it while lighting up the country's first nationwide 5G network and working to close our merger with Sprint," Legere said in a statement. "7 million net customers have chosen to join the Un-carrier movement in 2019, and they are choosing T-Mobile because we treat them right, we eliminate their pain points, and we are changing the rules of this industry for customers everywhere."

Regulators have already signed off on the merger, and the companies are awaiting a federal judge's decision after numerous state attorneys general sued to block the deal on anticompetitive grounds. Analysts believe the blockbuster combination will ultimately be allowed to proceed. Judge Victor Marrero is expected to issue a ruling as early as next month. Legere is resigning at the end of April once his contract is up.

Boosting guidance all year

T-Mobile added 4.5 million branded postpaid net additions in 2019, an impressive achievement considering the fact that T-Mobile continuously boosted its full-year outlook throughout the year -- and still came in above that climbing guidance.

Date Issued

2019 Branded Postpaid Net Customer Additions Guidance

Feb. 7 

2.6 million to 3.6 million

April 25 

3.1 million to 3.7 million

July 25 

3.5 million to 4 million

Oct. 28 

4.1 million to 4.3 million

Data source: T-Mobile.

T-Mobile will release full fourth-quarter results in February, which is also when investors can expect the company's 2020 outlook.