T-Mobile (NYSE:TMUS) reported 1.3 million net postpaid adds during the final quarter of 2015, including 917,000 net postpaid phone customers, to finish the year with totals of 3.5 million net postpaid phone adds and 4.5 million overall net postpaid adds.

The country's third-largest operator last month telegraphed its quarterly earnings by releasing preliminary figures, and much of its solid earnings report today is unlikely to surprise many analysts. It saw a quarterly churn of 1.46 percent, slightly below Wall Street estimates of 1.51 percent and matching a recent Barclays prediction, and added 8.3 million net postpaid customers in 2015.

But some of its quarterly finances were unexpectedly strong. Earnings were 34 cents a share, far outpacing the average of 18 cents predicted by analysts compiled by Bloomberg and up nearly threefold year-over-year. Sales rose to $8.25 billion, beating estimates of $8.2 billion, and fourth-quarter net income came in at $297 million, more than doubling consensus estimates of $134.5 million.

CEO John Legere took to Twitter to crow about the earnings, tweeting that T-Mobile "took 108% of the industry's postpaid phone growth last year."

The report marks the sixth straight quarter T-Mobile has posted more than 1 million branded postpaid net customer additions, and the sixth time in the last eight quarters in which total net customer adds exceeded 2 million.

T-Mobile's momentum over the past two years is due largely to aggressive promotions including the "uncarrier" strategy the company has driven with programs such as Binge On, which has proved popular with users even as it draws criticism from net neutrality proponents. But the operator also emphasized the improvements it has made to a network that was once a major vulnerability. T-Mobile's LTE network now covers 305 million POPs, an increase of 5 million POPs from the prior quarter, and its geographic footprint doubled last year.

Additionally, the company said it is "rapidly deploying both Wideband LTE to add capacity" and Extended Range LTE to improve coverage and in-building access. This month it forged deals with "multiple parties" to acquire more 700 MHz A Block spectrum covering roughly 48 million POPs, which will increase its total low-band spectrum holdings from 210 million POPs to 258 million POPs.

The fourth quarter also saw T-Mobile refarm the last of its MetroPCS airwaves and integrate them into its network. It saw $21 million in decommissioning costs for the shutdown of the CDMA network during the fourth quarter, down from $193 million during the previous quarter

The operator said it expects its success to carry over through 2016, predicting it will add between 2.4 million and 3.4 million branded postpaid net customer additions this year. On average, analysts compiled by Bloomberg say T-Mobile will add 3.28 million new subscribers this year.

Here's a closer look at some key quarterly metrics from T-Mobile:

Subscribers: As expected, T-Mobile added 2.1 million net customers and 1.3 million net postpaid adds, bringing its overall customer count to more than 63 million at the end of 2015. And the company saw 469,000 net prepaid adds during the quarter to complement its postpaid gains. The continued progress is particularly impressive given a U.S. smartphone market that has begun to stagnate.

Financials: Wells Fargo Securities noted that T-Mobile's total revenue, EBITDA and diluted EPS all exceeded Wall Street estimates "even after stripping out $194 million in leasing revenue." MoffettNathanson observed that adjusted service margin of 34.8 percent "handily beat consensus of 31.1 percent and was up 500 basis points year-over-year. T-Mobile is ultimately a free cash flow story, and 2017, not 2016, will be its starring year."

LTE: The carrier continued to make 4G a priority in 2015, doubling the geographic size of its LTE network and covering 305 million POPs by the end of the year, surpassing its goal of 300 million. The operator said the network will remain a focus in 2016 as it reaches further into suburban and rural markets, supporting that expansion with new retail distribution.

Churn: Branded postpaid churn was 1.46 percent, roughly in line with analysts' estimates and down 27 bases points year-over-year. T-Mobile credits its aggressive deployment of VoLTE and supporting handsets with helping to stabilize churn.

IoT: The operator is becoming more vocal about its IoT business, with executives spending several minutes on the call explaining how its strategy of migrating voice customers off of GSM is freeing up those networks for M2M services. T-Mobile believes the move will pay dividends in the IoT space over the at least the next two years, although it said it is also actively moving some M2M users onto LTE.

Summary: U.S. carriers are increasingly having to choose to focus either on growing their user base or on maximizing revenues. T-Mobile's subscriber growth was roughly what analysts expected, but its strong financials surprised many. As it continues to build out LTE and move into newer technologies, one looming question is whether it can continue to find ways to exploit its position as a disruptive "uncarrier."

Special Report: Wireless in the fourth quarter of 2015

For more:

- see this T-Mobile press release

- see this Bloomberg report

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