How to create a dialog like Twitter in programming?

You'd have to make sure your app is Universal (of course) and this is how I load my credits modal dialog...

Code:

    BOOL deviceIsPad = (UI_USER_INTERFACE_IDIOM() != UIUserInterfaceIdiomPhone);
    
    AppCredits *appCredits = nil;
    
    if (deviceIsPad) {
        appCredits = [[AppCredits alloc] initWithNibName:@"AppCredits_iPad" bundle:nil];
        [appCredits setModalPresentationStyle:UIModalPresentationFormSheet];
    } else {
        appCredits = [[AppCredits alloc] initWithNibName:@"AppCredits_iPhone" bundle:nil];
    }
    
    [self presentModalViewController:appCredits animated:YES];

This shows the modal view full screen on the iPhone and in a smaller Presentation Form Sheet on the iPad.

Hope that helps!