T-Mobile, the fourth-largest mobile operator in the US, bagged its best-ever quarterly haul of postpaid net additions – 1.38 million in the three months ended September – but the rising cost of attracting more subscribers has squeezed margins and dented profits.

Total Q3 operating expenses leapt 14 per cent year-on-year, to $7.3 billion, fuelled by higher SG&A (selling, general and administrative) and cost of equipment sales.

Operating income slumped from $297 million (Q3 2013) to $49 million, while its net loss widened from $36 million to $94 million over the same period.

Chief executive John Legere (pictured), speaking after Q3 financials were released at the inaugural Code/Mobile conference (organised by Re/code), seemed untroubled by the margin squeeze. “We’re kicking the shit out of the industry,” he said in his trademark no-holds barred style.

Under Legere’s stewardship T-Mobile is indeed enjoying unprecedented levels of subscriber and service revenue growth, and there was no sign of let-up during Q3.

Total branded postpaid customers numbered 25.9 million as of 30 September, up 1.38 million over the quarter, while the total branded prepaid customer base stood at just over 16 million (up 411 million since end June).

Third-quarter service revenue grew 10.6 per cent, year-on-year, to $5.7 billion. Total turnover (which includes equipment sales) was up nearly 10 per cent, to $7.35 billion.

T-Mobile boasted, too, that it had already reached its end-year target of covering 250 million of the US population with its LTE network.

“We’re now on track to cover 280 million people with 4G LTE by mid-2015, and we expect to hit the 300 million mark by the end of 2015,” said Neville Ray, T-Mobile’s CTO.

LTE expansion, added Ray, would be done by lighting up 700MHz and 1900MHz PCS spectrum, as well as by a continued push on the operator’s AWS spectrum.

Legere, speaking at the Code/Mobile conference, acknowledged that customer acquisition had come at a high cost, but still reckoned continued strong growth was sustainable for the foreseeable future.

It might be a hard task, however, to keep up with the impressive pace of growth set by the outspoken T-Mobile boss. Over the last six quarters alone, the operator has added 10 million customers.

As of 30 September 2014, T-Mobile had around 52.9 million customers (including 10.9 wholesale customers). When Legere took the helm in September 2012, T-Mobile had just over 30 million customers.