iPhone is the smartphone range designed and distributed by Apple Inc. since 2007. The iPhone has its own Operating System, iOS, and its latest version is iOS7.
The major iPhone feature is the application ecosystem invented by Apple.
An iPhone (or iPod Touch) application is a software, either free or at a set cost, you install on your device from the AppStore (Apple applications store).
The main goals when donwloading an app are:
- having fun, playing games (over 260,000 games and entertainment apps are available in the AppStore),
- buying a product, booking a service (m-commerce is planned to weight 13 billion euros in 2015 vs. 500 million in 2010!),
- listening to music, watching videos, reading news,
- finding out the appropriate service close by your location (transport, hotel, restaurant, point of sale, branch...)

A few numbers:
- More than 500 million iPhone distributed over the world (in March 2014)
- More than 1 million iPhone applications (beginning 2014)
- 60 billion download in october 2013 (x2 in 16 months)
- Market Share of 15.2% (-3.5pp) in 2013 vs. 78.6% for Android, Google OS.

iPhone and iPod Touch applications can integrate Apple native graphical components, already implemented in the existing Apple applications. They can exploit the full range of features embedded in the device : the multi-touch screen, the accelerometer, the 3D rendering engine, the compass, …
An application can launch native Apple applications for writing down an email, browsing an Internet page, taking a picture, or making a phone call.
Key success factors for an iPhone application are on the one hand a very good working knowledge of the iOS SDK and on the other hand a very good experience of ergonomics for touch-screen devices.
The user experience needs to be intuitive, natural, comfortable,...
Some prerequisites need to be integrated into the design and the development of the application, such as the limited volume of the application, the delay for pages loading, battery life-time management...