President-elect Donald Trump, accompanied by SoftBank CEO Masayoshi Son, speaks to members of the media at Trump Tower in New York, Tuesday, Dec. 6, 2016. Andrew Harnik | AP

The pair did not give details on what specific investments SoftBank would make, though Son suggested the Japanese company would target the technology sector. Sprint and T-Mobile shares popped after the news, but gave up most of those gains. Son has previously expressed interest in combining the companies, hoping to take on larger rivals, but he has faced regulatory resistance. The paperwork from Trump's meeting with SoftBank also featured the logo of Foxconn, also known as Hon Hai, a supplier for Apple's iPhones, Son noted. It was unclear what role the company would play in the deal.

