The company, which is controlled by Germany's Deutsche Telekom AG, added 1.65 million net new customers during the recent quarter, raising its total for the year to 4.4 million.
The quarter's total included 869,000 long-term, good-credit customers. And of that number, 800,000 were related to phones while 69,000 stemmed from tablets and other kinds of mobile devices.
These so-called post-paid customers are more lucrative and stable for wireless carriers. Elsewhere in the wireless industry, these are known as contract customers, but T-Mobile ended traditional two-year contract requirements when it introduced new pricing plans in March 2013.
T-Mobile has been working to take customers away from larger carriers such as Verizon and AT&T. During the recent quarter, the company began offering free data and texting abroad, along with a limited amount of free data each month for tablet owners.
For the current year, the company said it expects net additions of between 2 million and 3 million long-term, good-credit customers.
For the quarter ended Dec. 31, T-Mobile's loss totaled $20 million, or 3 cents per share, compared with a loss of $8 million, or 1 cent per share, in the same quarter of 2012.
Revenue increased 39 percent to $6.83 billion from $4.91 billion.
Service revenue jumped 25 percent to $5.17 billion, largely as a result of the inclusion of a full quarter of MetroPCS results, while revenue from equipment sales more than doubled to $1.58 billion.
For the full year 2013, T-Mobile earned $35 million, or 5 cents per share, compared with a loss of $7.34 billion, or $13.70 per share, in 2012. Revenue rose to $24.42 billion from $19.72 billion.