Sprint Says It Is in Negotiations With SoftBank of Japan Two giants overwhelmingly dominate the wireless market in the United States. Now a merger deal is in the works that could produce a robust challenger. Sprint Nextel said Thursday that it was in discussions with SoftBank over a "potential substantial investment." The talks, which began this summer, center on SoftBank, a Japanese telecommunications company, paying $12.5 billion for a stake of about 70 percent in Sprint, according to a person briefed on the matter who was not authorized to speak publicly. The talks emerged just a week after Deutsche Telekom, the parent of T-Mobile USA, announced a reverse takeover of another smaller company in cellphone service, MetroPCS . The spate of deal-making is aimed at shifting the balance of power in a United States market largely controlled by Verizon Wireless and AT&T. They have more than 200 million customers -- more than their next six competitors combined. Article Tools Related Links As the No. 3 cellphone service provider, Sprint, with more than 56 million subscribers, has long struggled to catch up. In recent years, it has sought to compete primarily on price. But the T-Mobile-MetroPCS merger could create a tougher competitor in the lower end of the cellphone market. While Sprint has committed billions of dollars to revamping its infrastructure, hoping to develop a Long Term Evolution high-speed network, it has been constrained by limited financial resources. Sprint carried nearly $21 billion in long-term debt as of June 30, and