Google has launched in-app billing for Android apps, company executive Eric Chu announced in a blog post yesterday.

In-app billing will let Android users make purchases of digital goods like media files or upgrades for mobile games without exiting the app. The in-app billing service is handled by Google's Android Market.

Several Android apps are already offering the service, including Tap Tap Revenge by Disney Mobile; Comics by ComiXology; Gun Bros, Deer Hunter Challenge HD and World Series of Poker Hold'em Legend by Glu Mobile; and Dungeon Defenders: FW Deluxe by Trendy Entertainment.

Niccolo de Masi, CEO of Glu Mobile, called the start of in-app purchases on Android Market a "very significant step forward."

"The Android gaming market continues to demonstrate impressive growth and we are optimistic that over the medium term in-app payments on Android will generate revenue streams analogous to those on iOS," de Masi said, referring to Apple's rival operating system for the iPhone and iPad.

Apple launched in-app payments in 2009. Four of the 10 highest-grossing apps in the App Store – Tap Zoo, Smurfs' Village, Zombie Farm and Texas Poker - are free but allow in-app purchases. The launch of in-app payments on Android could help developers make more money off apps for the competing operating system.

Apple's in-app payments generated concern after children using their parent's iPhones racked up huge bills buying digital goods through games like Smurfs' Village. Apple has since changed how purchases within iOS games are authorized.