Coinciding with Softbank’s stock earnings release today, Zynga has finally put out a press release confirming a $150 million investment from the Japanese tech giant. The partnership first came to light through VentureBeat in April, and by last month a $147 million investment was being reported.

Although there’s not much new in the release, it does note that Zynga will “leverage Softbank’s cutting edge mobile and Web technology,” which confirms that Zynga not only intends to localize its existing games but also work to tap into Japan’s lucrative mobile market.

Taking a mobile-heavy approach in Japan makes sense for the market, but it could also have implications for Zynga’s operations at home.

Since Softbank is the only distributor of the iPhone in Japan, it’s reasonable to expect that Zynga will be porting its games to that platform (besides which, many Japanese feature phones wouldn’t be suitable for Zynga’s games). It would make sense, in that case, for Zynga to release any iPhone versions of its games not only in Japan, but in its other home markets.

Zynga has put very little effort into mobile in the United States, with the recent exception of FarmVille’s release on the iPhone; however, we did recently notice that the company was hiring for a high-level mobile management position.

So far, there’s still no official word on the exact amount of Zynga’s investment from Google, which was reported as being $100 to $200 million earlier this month.