Shares of MetroPCS, based in Richardson, Texas, dropped 40 cents, or 3.3 percent, to $11.64, as investors speculated that Softbank's interest means there's less of a chance for a counterbid from Sprint.
Tokyo-based Softbank, once the underdog in Japan's telecom industry, has seen its fortunes improve ever since it started selling the iPhone in 2008. It was initially the only Japanese phone company to offer the iPhone. Rival KDDI Corp. started selling the iPhone late last year.
The U.S. wireless industry is no stranger to foreign investment, but the results have been mixed. T-Mobile is owned by German phone company Deutsche Telekom. With T-Mobile treading water, DT has tried to exit its investment by selling the subsidiary to AT&T. That deal was scuttled by U.S. regulators.
Vodafone Group PLC, a British cellphone company, owns 45 percent of Verizon Wireless. That's been a successful investment, but New York-based phone company Verizon Communications Inc., which owns the rest, has complete control over the joint venture and is seen as having twisted Vodafone's arm in an attempt to get it to let Verizon take complete ownership.
Shares of Clearwire Corp. jumped 92 cents, or 70.1 percent, to $2.22 on news of the Softbank talks. Sprint owns half of the company, and investors were betting that a deal with Softbank would include a buyout of Clearwire. The company operates a wireless broadband network that Sprint resells as "Sprint 4G." Clearwire has struggled to become a viable standalone company, and it needs additional funding to upgrade its network.
Associated Press writers Michelle Chapman and Barbara Ortutay contributed to this story.