“There’s an app for that” is Apple’s catch phrase to promote the literally thousands of applications that can be downloaded to an iPhone. Whether you want to check the weather or traffic, bide time playing a game, or study a new language, there is likely a free or paid application that you can access. While Apple may be best known for mobile apps, BlackBerry, Android and other devices also have a huge range of apps available in their stores, as well as in those operated by mobile service providers. With smartphones expected to overtake feature phones in the U.S. by 2011, the popularity of mobile apps will only grow. To get a better sense of what’s popular and what’s not now, Nielsen recently launched its ‘App Playbook,’ surveying more than 4,200 people who had downloaded an application in the past 30 days.