What you're seeing in contacts is the standard presenting of a modal view controller (UIViewController documentation). Rather than using pushViewController:animated use
Code:
presentModalViewController:animated:
&
dismissModalViewControllerAnimated:
to get that effect. You can read more in the UIViewController documentation & decide if it's appropriate to use a modal controller.
As far as just overriding UINavigationBar animations, a search will get lots of examples on doing it.