A new forecast from International Data Corporation (IDC) says that mobile app downloads will increase from 10.7 billion in 2010 to 182.7 billion in 2015.

A shift to a rapidly growing focus on in-app purchasing to fund business models from the current, near-total reliance upon initial app download purchases as the primary focus of app monetization has been experienced, the IDC report said.

The shift is most visible in the free app category, where in-app purchases allow users to to turn on additional features or buy a more functional version of the app.

IDC vice president of Mobile and Connected Consumer Platforms Scott Ellison said app developers are not only focusing on ways to ‘appify’ just about every interaction you can think of in your physical and digital worlds, they are now focusing on longer term sustainability issues.

"The user sustainability trifecta of social networking, location, and the cloud are now increasingly being supported by the business model financial trifecta of application store purchases, in-app purchasing, and in-app advertising," Ellison said.

The report said users will be more engaged, both within the app itself and over time, if business models seek to include in-app purchasing and in-app advertising.

Together these dynamics are driving significant shifts in how apps are conceptualized, the integration of additional services and features like social networking and location to more deeply engage users, and how apps are actually developed in terms of incorporating in-app purchasing, IDC said.