.h:
UIActivityIndicatorView* progressView;
.m:
// show the waiting symbol
progressView = [[UIActivityIndicatorView alloc]
initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
[progressView setCenter:CGPointMake(160.0f, 240.0f)];
[progressView startAnimating];
[self.view addSubview:progressView];
// dismiss the waiting symbol
[progressView removeFromSuperview];
[progressView stopAnimating];
[progressView release];