BELLEVUE. Wash. ( TheStreet) -- T-Mobile USA, a unit of Deutsche Telekom ( DT), said Wednesday that President and CEO Robert Dotson will step down next year. Philipp Humm, a former CEO of T-Mobile Deutschland, will be Dotson's successor. Humm is currently responsible for sales and service in Europe as chief regional officer. Humm will take over as CEO of T-Mobile USA in February, the company said in a press release. T-Mobile USA is the fourth-largest U.S. mobile operator. It has seen revenue and earnings decline partly because of increased competition. T-Mobile USA saw customer numbers decline by 77,000 in the first quarter "as a result of the intense competitive environment and an industry-wide downturn," Deutsche Telekom said when its earnings were reported earlier this month. -- Reported by Joseph Woelfel in New York. Follow TheStreet.com on Twitter and become a fan on Facebook.