Sprint Nextel (NYSE:S) has found a Japanese sugar daddy.

We've known for a couple of weeks that America's third-largest wireless network provider has been talking to Japanese counterpart Softbank about a cash-infusion deal.

Today, a press release from Softbank shows that the talks have resulted in a solid agreement. It's not an outright acquisition, but a very large equity investment that would give Softbank 70% ownership of Sprint. The deal is expected to breeze through regulatory reviews and close in mid-2013.

If given the go-ahead on both sides of the Pacific, Softbank will pay $8 billion up front for a slug of freshly minted Sprint shares, and then take $12 billion of existing stock off the hands of current shareholders. The company will pay $7.30 per share, a 27% premium to Friday night's closing price.

Sprint shares are surging nearly 10% on the pre-market news, but Clearwire (NASDAQ: CLWR) is jumping 25%. That company lives and dies with Sprint, but lives much closer to the edge of insolvency, so this deal is seen as a lifesaver for both Sprint and Clearwire. A Sprint on more stable financial footing may even try to acquire Clearwire outright.