[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(called:) name:@"UIApplicationSuspendedNotification" object:nil];
-(void)called:(NSNotification *) notification
{
NSLog(@"Tapped Call button");
}
if Call button was tapped then application will be terminated and go into background so just add an observer for the UIApplicationSuspendedNotification
notification.