A decade of operational problems has considerably diminished Sprint's position in the wireless industry. It is now the fourth-largest carrier in the United States, serving 26 million postpaid and 9 million prepaid phone customers directly and 13 million via wholesale channels. Over the past five years, the firm's share of the postpaid phone market has declined about 1 percentage point to 12%, leaving it about three fourths the size of T-Mobile U.S., the next smallest carrier. About 4% of sales come from the wireline unit, which provides phone and data services to the wireless unit and external customers. Japanese firm Softbank took a 78% stake in Sprint through the purchase of existing Sprint shares and a $5 billion equity infusion in 2013; it has since increased its stake to 85%.