Japanese mobile social firm DeNA has announced that it has taken a 20% stake in US iPhone social games company Aurora Feint.

It's a big deal in the mobile games world. DeNA runs the Mobage Town mobile games service in Japan, which has more than 15 million users and generates $200 million of annual revenues.

Meanwhile, Aurora Feint is behind the OpenFeint platform, which is being used by more than 200 iPhone games to provide Xbox Live-style social features, with 500 more in development.

How do Mobage Town and OpenFeint fit together? Well, that's a bit unclear right now, but if it means a two-way flow of features and technology, it's a potentially powerful partnership for both companies.

As part of the deal, DeNA will be promoting OpenFeint to its partners in Japan, with one - games publisher Hudson - already agreeing to use Aurora Feint's community tools in its iPhone games going forward.

"We look forward to a longterm partnership which will bring the synergy of our experience in operating large mobile social networks, and the experience of OpenFeint in operating a large social gaming platform in the smartphone market."

With competition fierce in the iPhone social game platform market, the deal further cements Aurora Feint's position as one of the leaders.