The status bar in an iphone application shows the network connections (Telco, WIFI, bluetooth.. etc), date, battery usage, location icon... etc.
For some application, it may be usefull to hide the status bar so that the application has maximum screen area.
To hide the status bar, send the setStatusBarHidden message to the UIApplication object. It should be send in the UIApplication's didFinishLaunchingWithOptions method. This method will be invoked when the application finish launching.