SoftBank Corp, the Japanese mobile carrier with ambitious plans to grow overseas, slashed its profit forecast as Sprint Corp, the U.S. carrier it bought for $21.6 billion, continues to lose customers with no quick fix in sight. In a statement on Tuesday, SoftBank said it now expects an operating profit of 900 billion yen in the 12 months through March 2015, 10 percent down from the 1 trillion yen profit it previously estimated, citing Sprint's troubles.