(Telecompaper) Apple announced that customers spent over USD 10 billion on its App Store in 2013, including over USD 1 billion in December alone. App Store customers downloaded almost three billion apps in December, making it the most successful month in the App Store's history. Apple said developers active on the store have now earned USD 15 billion. In total more than 1 million apps are available on the Apple store, to users of the iPhone, iPad and iPod touch in 155 countries around the world.