The Japanese mobile phone carrier Softbank has reached a deal to buy 70 percent of U.S. wireless company Sprint Nextel. The $20 billion deal is the largest-ever Japanese acquisition of a foreign company.

Sprint is the third largest mobile carrier here in the U.S. Verizon and AT&T each have roughly twice as many customers. One reason? They’ve been a lot quicker to build their high-speed 4G networks.

“That’s what customers want. They want the speed,” says analyst Jeff Kagan.

Sprint is in the middle of its own $7 billion network upgrade. Kagan says the deal with Softbank would give the company much-needed cash to move faster on its conversion to 4G. “They’re just moving into it at a glacial pace,” Kagan says. “This is going to help them immensely.”

Shareholders and regulators must first approve the deal with Softbank. Kagan says the approval process will take longer with a foreign company involved.