KDDI Corp. confirmed plans Sunday to enter the U.S. market where it would offer cell phone services through a network lease agreement with Sprint Nextel. The announcement by KDDI, Japan’s second-largest wireless operator, comes as the company continues its overseas expansion in the midst of an increasingly competitive and saturated market at home. Although KDDI’s plan follows on rival NTT DoCoMo’s $10 billion investment in AT&T that was completed in 2001, KDDI would become the first Japanese telecom company to operate under its own brand name within the U.S. The service, dubbed “KDDI Mobile,” will be targeted primarily to Japanese customers in the U.S. and will feature Japanese language input and other functions used by KDDI customers in Japan. KDDI would offer the service through KDDI America, its U.S.-based unit, possibly as early as this month.