T-Mobile faced severe iPhone 5s constraints in Q3 2013, limiting sales at launch [u]

While T-Mobile refused to provide actual sales figures for the iPhone during the carrier's quarterly conference call, Chief Marketing Officer Mike Sievert said Apple's devices accounted for about 15 percent of the 3.6 million phones sold under the T-Mobile brand, according to AllThingsD. The resulting sum is a significant step down from sales posted by Sprint and Verizon, who moved 1.4 million and 3.9 million iPhone units, respectively, in the same period.

Despite the low volume, T-Mobile deemed the launch of Apple's new flagship iPhone 5s and mid-range iPhone 5c "successful" and cited the launch, together with sales of the iPhone 5 prior to the new models' introduction, as key drivers of the carrier's nearly $1 billion year-over-year jump in handset revenues. Overall smartphone shipments made a similar leap, from 2.3 million one year ago to 5.6 million in the third quarter.

Deutsche Telekom-backed T-Mobile has made Apple devices a focal point of its turnaround strategy in recent months. The carrier began selling the iPhone 5 in June and was a launch partner for the iPad Air earlier this month, offering 200 megabytes of mobile data per month to all owners of Apple's tablets.

Update: Following the conference call, T-Mobile told AllThingsD that the carrier sold more tablets on iPad Air launch day than it did during the entire preceding quarter. As it did in relation to iPhone sales, T-Mobile declined to be more specific.

After languishing in fourth place for years and in the aftermath of a failed acquisition by AT&T, T-Mobile has been making strides against its larger rivals. The third quarter brought 1 million net new customers on a 6 percent jump in earnings to $1.3 billion.