UIProgressHUD is a view which occupies the whole window for showing a short progress message. This view is private, that means you shouldn't use them for AppStore apps, but alternatives exist.
Also note that UIProgressHUD is just a normal view. It will not block interactions to other background views.
UIProgressHUD* hud = [[UIProgressHUD alloc] initWithFrame:CGRectZero]; [hud setText:@"Loading, please wait."]; [hud showInView:someView]; ... [hud done]; ... [hud hide]; ... [hud release];
- MBProgressHUD: http://github.com/jdg/MBProgressHUD