When a call is first received the app delegate is sent a applicationWillResignActive:
message while the system displays the incoming call dialog.
If the user refuses the call, the app delegate receives an applicationDidBecomeActive
message and the app can resume.
If user accepts the call, the app delegate receives an applicationWillTerminate
message and you should prepare the app for shutting down. Then the system shuts down the app.
You can't force the system to restart your app after a call completes.
If none of these methods are being called in the delegate, the most likely explanation is that you don't have the delegate assigned properly.
It sounds like you might be confusing your app delegate with one of your view controllers. An app delegate is not expected to respond to 'viewDidLoad' an other UIViewController messages.
Edit01:
Upon second reading, it sounds like you want the app to resume the state it had prior to quitting in response to taking a phone call.
If so, your not really looking to trap an event. When an app restarts following a call, it does not receive a special event i.e. it starts just as it would if the user launched it. I think what you need to do is save the state of the application prior to shutting down and then reset to that state the next time it starts up.