Apple does support this for the presentation of modal views as of 3.2. This makes sense: the page curl effect is intended to signal the user that a page of options or settings is being revealed, and when they are done changing things, they will be sent back to the original view. Apple doesn't want the animation to infer an ongoing change to the page hierarchy, just a modal one that must return to its starting place.
It's pretty straightforward to use; just be sure that you are starting from a full screen view, and loading with the UIModalPresentationFullScreen style, which I believe is the default.
There are animation transitions to use a similar effect in UIViews generally that were added as of 4.0, but this is a straightforward way to use the effect.
simpleVC * myModalVC = [[simpleVC alloc] init];
[myModalVC setModalTransitionStyle:UIModalTransitionStylePartialCurl];
[myModalVC setDelegate:self];
[self presentModalViewController:myModalVC animated:YES];
[simpleVC release];
Link to Apple Docs on UIModalTransitionStyle constants
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