It’s been hard for social media sites serving consumers to monetize their popularity. (The exception, of course, is LinkedIn, which occupies the B2B space.)However, it looks like gaming applications hosted on social media sites may be having more success, and through subscription-based business Models, no less.The popular Facebook game FarmVille (owned and operated by Zynga), just announced that it’s rolling out a beta version subscription plan. Current FarmVille fanatics can convert their coins into Farm Cash, which will be used to “pay” for the subscription offering. If the beta testing indicates high interest, the company plans to roll out a monthly subscription plan priced at $10.This is an interesting development in the online subscription industry. I’ve long said that social media sites can’t monetize through direct consumer spending — no one logs onto Facebook in order to spend money, and there’s too much free competition in the social media market. However, monetizing interactive gaming can be highly lucrative.Games like FarmVille require the interactivity and public forum of social media networks. And I suspect that most people like playing games with people they know, not strangers with weird “handles.” And since the game is purely for entertainment purposes (not communication and connection, the key benefit of Facebook’s other features), people will have less resistance to paying.In addition, the games are addictive and require long-term investment for success, making subscription billing the perfect revenue Model.