Zong is rolling out a subscription service, where users can sign up to buy premium features in online games and on web sites and pay via their mobile phone accounts. Along with a variety of other companies, Zong already lets users pay for virtual goods via their mobile phones, so this is a new way for customers to pay and for merchants to make money.

Flagship members of the subscriptions service include photo and video-sharing site Photobucket and social gaming site OMGPOP.

Zong lets people enter their ten-digit phone numbers online, get a four-digit confirmation PIN number by text message, then enter that number online to finish the purchase. Fees appears on the user’s monthly phone bill.

Mobile subscriptions, unfortunately, have been associated with online scams, where users get tricked into buying subscriptions within quizzes or other simple games. We asked Zong about this, and here’s what chief executive David Marcus told us:

As to the concern about “scammy” ringtones providers, we are looking to raise the standards here and build a brand that consumers know and trust, ZONG. We vet each and every ZONG merchant and don’t work with any scam artists or other unsavory businesses.  Our customers are “blue chip” providers or digital good and services.

Zong also recently launched mobile payment tests for virtual currency with Facebook. The subscription service will first roll out in the US, then expand to Canada, Australia and Europe in the coming months.