T-Mobile USA is cutting 7% of its staff, part of an effort to rein in costs as the company spends heavily to attract new subscribers in an increasingly competitive market. From a report: The move will affect about 5,000 positions, mostly corporate and back-office staff along with some technology roles, T-Mobile said in a regulatory filing. Retail and consumer-care experts won’t be impacted. Chief Executive Officer Mike Sievert said in a letter to employees that the cost of attracting and retaining customers is “materially more expensive than it was just a few quarters ago.” Building out the company’s high-speed internet business and efforts in other areas “is not enough to deliver on these changing customer expectations going forward,” he said.