Those reports from last week are now official, and it looks like the deal has been made. Softbank plans to buy a 70% stake in Sprint for around $20 Billion ($12.1 billion in cash consideration & $8 billion in capital). Now, the deal just has to pass through U.S. Federal approval. Most of the industry intel indicates that the deal is likely to be pushed though and approved very quickly, because it is "pro-competitive" rather than anti-competitive. Softbank has a history of taking second tier carriers and improving their competitiveness. This deal will likely net Sprint an extra $3 Billion in extra cash that they can use to bolster their network significantly and deploy their new LTE tech more quickly. Here's a quote from Dan Hesse,
Assuming this merger/acquisition goes through, the name for the company will be changed to "New Sprint." Between Softbank and Sprint, their combined subscriber base will be one of the largest in the world. Also, they will have the third highest mobile service revenue of any global company. Hit up the source link below for the full press release.
Source: Softbank Officially Purchasing 70% of Sprint - Full Press Release