DeNA snagged another key partnership for its Mobage mobile gaming platform by signing up Glu Mobile. The deal brings Glu’s most prominent smartphone-based franchise Gun Bros on board.

The agreement also comes at a time of ruthless competition to become the leading mobile gaming platform, with companies like GREE and its subsidiary OpenFeint, PapayaMobile, Heyzap, Playphone and more vying for the crown. Plus companies like France’s Gameloft are planning to launch their own social networks.

The prize of this race is to be more than a standalone gaming company. It’s to become a platform that isn’t subject to the same ups and downs that hits-driven businesses are vulnerable to.

It’s also to reap all of the downstream revenues around payments that supporting multiple games from many developers might bring. DeNA and its rival GREE pioneered this model in Japan and are now trying to duplicate their success abroad. DeNA said in its most recently quarterly earnings report that its goal for the Mobage global platform was to reach $50 million in Moba-coin consumption during the quarter ending in March of next year.

To get there faster, the company bought Ngmoco for up to $403 million in 2010. DeNA stands as one of the most well-funded players in this race. Unlike purely venture-backed companies like Heyzap and PapayaMobile, DeNA has more capital to sweeten deals for third-party developers and is probably more willing to stomach losses over time to grab market share.

Even before the full public launch, DeNA had rounded up developers like Zombie Farm-marker Playforge and Tiny Tower-maker NimbleBit. Gun Bros is another big title to put on top of that. It brought in $1.5 million in revenue for Glu Mobile in the third quarter of this year. 

That said, DeNA is still behind schedule on its full Mobage launch. The company said in its most recent earnings statement that it expected the iOS version of the network to be out by November or December. It still hasn’t happened in the U.S., although it is out in China. Sources familiar with the matter have also told us that Ngmoco is unlikely to make its $100 million earnout based on performance by the first half of this year and as of last quarter.