Shares of Japan’s SoftBank (Tokyo: 9984)  plunged nearly 20 percent Friday after Sprint-Nextel Corp. (NYSE: S) said it was “in discussions” about selling Softbank a majority stake.

Softbank shares closed down 17 percent at 2,395 yen (USD: $30.54) in Tokyo trading. Shares of Sprint fell 16 cents to $5.60 in pre-market trading after leaping 15 percent on Thursday.

Acquiring what could be a 70 percent stake in Sprint, the No. 3 U.S. telecommunications carrier, might cost as much as $17 billion, bankers said. Softbank has long-term debt of $10 bilion, largely incurred from prior acquisitions.

Reuters reported Softbank was in talks with a Japanese bank syndicate about financing a deal. The banks include Mizuho Financial, Sumitomo Mitsui Financial Group and Mitsubishi UFJ Financial Group.

Softbank has confirmed its ambitions for Sprint, of Overland Park, Kan., but hasn’t been more specific. If it were to bid for Sprint, it would likely also partner with U.S. institutions, many of which have dealt with Sprint and its predecessor company, founded in 1899.

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