Japan's SoftBank Corp said on Tuesday its third-quarter operating profit slid 5.9 percent, missing estimates, as the ambitious mobile telecom firm continues to soak up the cost of trying to turn around loss-making U.S. unit Sprint Corp. SoftBank, which took over the number 3 U.S. carrier for more than $20 billion in 2012, said October-December operating profit was 191.39 billion yen , down from 203.46 billion yen a year ago. That trailed the 219.08 billion yen average of five analysts' estimates compiled by Thomson Reuters StarMine.