With the rise of social applications and virtual goods on Facebook and other social platforms, established competitors are moving in to do business. The latest is Mopay, a decade-old European mobile payments company. It’s opening a new US office in Palo Alto, near to Facebook’s headquarters and many developers of social games.

Mopay is competing directly against companies like Boku and Zong by making it easy for people to charge their phones and pay for small amounts of virtual currency in games and other apps. While it has developed a range of mobile messaging and payments interfaces, the Mopay process is similar to its competitors in terms of what you’ll see on Facebook. A user picks Mopay as a payment option within an app, typically in an offer wall, provides a phone number, receives a mobile payment confirmation number via text, and enters that number in the app to receive the currency.

The company already has deals in place with European game developers, including Bigpoint, Gameforge, Innogames and Sulake. The move to the US is both intended to bring in new customers for existing clients, and help Mopay partner with more US-based developers who have users in Europe and around the world. Overall, Mopay has deals in 65 countries and reaches more than 500 million people worldwide.

We’ll keep tracking the space as competition heats up to power mobile payments inside Facebook apps and social games.