Just as an app utilizes different storyboards for iPad and iPhone, I would like my app to use a different storyboard for the iPhone 5. Since there is no option in the Info.plist to select default storyboard for iPhone 5, how would I programmatically call the storyboard?
I do not want to use AutoLayout for this app unless it is absolutely the last resort. I understand how to detect if a user is using an iPhone 5 or other device with the same screen size. I just need to know how to set the default storyboard without the plist.
I was looking for the same answer couple of weeks ago here's my solution hope helps..
-(void)initializeStoryBoardBasedOnScreenSize {
    if ([UIDevice currentDevice].userInterfaceIdiom == UIUserInterfaceIdiomPhone)
{    // The iOS device = iPhone or iPod Touch
    CGSize iOSDeviceScreenSize = [[UIScreen mainScreen] bounds].size;
    if (iOSDeviceScreenSize.height == 480)
    {   // iPhone 3GS, 4, and 4S and iPod Touch 3rd and 4th generation: 3.5 inch screen (diagonally measured)
        // Instantiate a new storyboard object using the storyboard file named Storyboard_iPhone35
        UIStoryboard *iPhone35Storyboard = [UIStoryboard storyboardWithName:@"Storyboard_iPhone35" bundle:nil];
        // Instantiate the initial view controller object from the storyboard
        UIViewController *initialViewController = [iPhone35Storyboard instantiateInitialViewController];
        // Instantiate a UIWindow object and initialize it with the screen size of the iOS device
        self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
        // Set the initial view controller to be the root view controller of the window object
        self.window.rootViewController  = initialViewController;
        // Set the window object to be the key window and show it
        [self.window makeKeyAndVisible];
    }
    if (iOSDeviceScreenSize.height == 568)
    {   // iPhone 5 and iPod Touch 5th generation: 4 inch screen (diagonally measured)
        // Instantiate a new storyboard object using the storyboard file named Storyboard_iPhone4
        UIStoryboard *iPhone4Storyboard = [UIStoryboard storyboardWithName:@"Storyboard_iPhone4" bundle:nil];
        // Instantiate the initial view controller object from the storyboard
        UIViewController *initialViewController = [iPhone4Storyboard instantiateInitialViewController];
        // Instantiate a UIWindow object and initialize it with the screen size of the iOS device
        self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
        // Set the initial view controller to be the root view controller of the window object
        self.window.rootViewController  = initialViewController;
        // Set the window object to be the key window and show it
        [self.window makeKeyAndVisible];
    }
    } else if ([UIDevice currentDevice].userInterfaceIdiom == UIUserInterfaceIdiomPad)
    {   // The iOS device = iPad
    UISplitViewController *splitViewController = (UISplitViewController *)self.window.rootViewController;
    UINavigationController *navigationController = [splitViewController.viewControllers lastObject];
    splitViewController.delegate = (id)navigationController.topViewController;
    }
}
Call this method under AppDelegate ddiFinishLaunchingWithOptions: method And also don't forget the name your storyboards properly
Hope helps...
This worked for me - slight refinement with wrapping getting the storyboard in a function
-(UIStoryboard*) getStoryboard {   
    UIStoryboard *storyBoard = nil;
    if ([UIDevice currentDevice].userInterfaceIdiom == UIUserInterfaceIdiomPad) {         
        storyBoard = [UIStoryboard storyboardWithName:@"MainStoryboard_iPad" bundle:nil];
    }else{
        if ([UIDevice currentDevice].userInterfaceIdiom == UIUserInterfaceIdiomPhone){
            // The iOS device = iPhone or iPod Touch
            CGSize iOSDeviceScreenSize = [[UIScreen mainScreen] bounds].size;
            if (iOSDeviceScreenSize.height == 480){
                // iPhone 3/4x
                storyBoard = [UIStoryboard storyboardWithName:@"MainStoryboard_iPhone_4" bundle:nil];
            }else if (iOSDeviceScreenSize.height == 568){
                // iPhone 5 etc
                storyBoard = [UIStoryboard storyboardWithName:@"MainStoryboard_iPhone_5" bundle:nil];
            }
        }
    }
    ASSERT(storyBoard);
    return storyBoard;
}
UIStoryboard* mainStoryBoard = [self getStoryboard];
    self.initialViewController = [mainStoryBoard instantiateInitialViewController];
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.rootViewController = self.initialViewController;
    [self.window makeKeyAndVisible];
来源:https://stackoverflow.com/questions/12696242/how-to-switch-to-different-storyboard-for-iphone-5