The secret to socializing and monetizing mobile gaming? There is none, considering it's long been used by online multiplayer goliath World of Warcraft, which counted 10.3 million subscribers last November. Nonetheless Eiji Araki, svp of social games at Japanese mobile gaming company GREE International, prescribed that game developers incentivize casual gamers to invite friends to play in order to grow a game's user base, and monetize hardcore gamers by having them pay to unlock new achievements or progress through a game's levels. "We have to make sure each segment of users has their role in the game," he said during an afternoon SXSWi session on Saturday. While GREE categorizes 95 percent of its 190 million global mobile users as casual gamers, Araki said the company generates 80 percent of its revenue from getting gamers to pay to play. GREE is able to divest its core gamers of their money because they "love to pay money to achieve something." It's the "freemium" business model fused with game mechanics. Araki recommended tapping into gamers' varied levels of competitivness: acclimate a casual gamer to perform actions like inviting a friend to play in order to access new features, then hope that person becomes so addicted that they're eventually willing to pay for further progress. Opportunistic as that may sound, it's sensible, as GREE's revenue and user numbers demonstrate. But whether it's a viable long-term strategy is another matter. Those World of Warcraft users numbers from November? Down 1.1 million gamers from March 2011