iAds interstitial adverts on iPhone?

I’ve also been waiting for interstitial ads for iPhone from iAd. I finally have it implemented into one of my apps and it is running and showing test ads just fine. The app is currently in review and I will update my answer once it is approved and I can test if any actual ads are being served. In the meantime, here is the code I used to implement iAd interstitials:

ViewController.h

@interface ViewController : UIViewController <ADInterstitialAdDelegate> {
    ADInterstitialAd *interstitial;
    BOOL requestingAd;
}

-(void)showFullScreenAd;

ViewController.m

-(void)viewDidLoad {
    requestingAd = NO;
}

// Interstitial iAd
-(void)showFullScreenAd {
    // Check if already requesting ad
    if (requestingAd == NO) {
        [ADInterstitialAd release];
        interstitial = [[ADInterstitialAd alloc] init];
        interstitial.delegate = self;
        self.interstitialPresentationPolicy = ADInterstitialPresentationPolicyManual;
        [self requestInterstitialAdPresentation];
        NSLog(@"interstitialAdREQUEST");
        requestingAd = YES;
    }
}

-(void)interstitialAd:(ADInterstitialAd *)interstitialAd didFailWithError:(NSError *)error {
    interstitial = nil;
    [interstitialAd release];
    [ADInterstitialAd release];
    requestingAd = NO;
    NSLog(@"interstitialAd didFailWithERROR");
    NSLog(@"%@", error);
}

-(void)interstitialAdDidLoad:(ADInterstitialAd *)interstitialAd {
    NSLog(@"interstitialAdDidLOAD");
    if (interstitialAd != nil && interstitial != nil && requestingAd == YES) {
        [interstitial presentFromViewController:self];
        NSLog(@"interstitialAdDidPRESENT");
    }
}

-(void)interstitialAdDidUnload:(ADInterstitialAd *)interstitialAd {
    interstitial = nil;
    [interstitialAd release];
    [ADInterstitialAd release];
    requestingAd = NO;
    NSLog(@"interstitialAdDidUNLOAD");
}

-(void)interstitialAdActionDidFinish:(ADInterstitialAd *)interstitialAd {
    interstitial = nil;
    [interstitialAd release];
    [ADInterstitialAd release];
    requestingAd = NO;
    NSLog(@"interstitialAdDidFINISH");
}

I just call -(void)showFullScreenAd after the user performs a certain action. For more information refer to UIViewController iAd Additions Reference

EDIT: 01/03/14
The app update was approved and has been live for 12 hours now. I still have not received any interstitial iAds as of this moment. It may be due to the lack of inventory for interstitial ads on iPhone or it may have something to do with the following message I’ve received in my iAd module on iTunes Connect. The message reads

When you submit your app, [app name], for approval, it will also be reviewed by iAd for use on the App Network to determine its appropriateness for receiving ads from iAd advertisers. Once your app is approved, you will be ready to start earning revenue for ads that run in your app.

I’ve never received this message before, I usually receive the “Your app is now eligible to receive ads” message as soon as the update is released in the App Store. It’s either because of the new implementation of interstitial ads in my app or Apple has updated some of its iAd procedures.

Will update answer again if and when I do start receiving interstitial iAds. In the meantime you may test it yourself on my app +Quotes. The above code is invoked and an interstitial ad should show once a user shares via Facebook within the app.

EDIT: 01/07/14
Contacted iAd directly and received a response today

Hello Daniel,
Initial fill rates will reflect the recent launch of interstitials on iOS 7. Thank you for your patience as we ramp up ad serving.
If you haven’t already, we recommend you integrate standard portrait and landscape iAd banners in your app to take advantage of all available types of advertising inventory.
Finally, for future reference, when you submit your app for approval, it will also be reviewed by iAd to determine its appropriateness for receiving ads from iAd advertisers. Therefore, it may take a few days for your new iAd enabled app to begin receiving ad impressions.
Best Regards,
 iAd App Network Support

So, interstitial iAds for iPhone do work with iOS 7.0 and above but have a low fill rate currently.