If you're using a UITabBar
/UITabBarController
, I think you must have the selectedIndex
set to some legal value. I don't think this is possible, nor can I find an app on my iPhone or iPod that mimics the behaviour you're looking for.
(The App Store app is as close as it gets, where it looks like it has an empty tab bar before it loads data from the Internet, but it could very well be that they are just re-using the Default.png and superimposing an activity indicator during loading.)
Note that if you tried to submit your app to Apple, they could easily reject it for using non-standard UI.