The easiest way to hide the status bar is to go into youInfo.plist; right click to add a row and select Status Bar Initially hidden.
This will ensure every time you app launches the status bar will be hidden.
Edit
with programming
[[UIApplication sharedApplication] setStatusBarHidden:YES withAnimation:UIStatusBarAnimationNone];
self.navigationController.navigationBar.frame = CGRectMake(0, 0, 320, 44);
and when you want to show the statusbar just use bellow code..
[[UIApplication sharedApplication] setStatusBarHidden:NO withAnimation:UIStatusBarAnimationNone];
self.navigationController.navigationBar.frame = CGRectMake(0, 45, 320, 44);
i hope this help you...
:)