iAds interstitial adverts on iPhone?

Question 1

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.

Question 2

My original answer is starting to age away so here's a newer Swift implementation:

This implementation uses a Manual ADInterstitialPresentationPolicy so we can present our interstitials at our own intervals. When manually presenting your interstitial it does not load with its own close button to dismiss itself. So, what I've done is created a UIView to present the interstitial in and used the interstitial's delegate methods to dismiss the UIView. The inconsistency with receiving an ad from the iAd network still arises when testing. Sometimes you receive an ad, sometimes it fails to load which allows us to request a new ad, and sometimes nothing happens at all. This just seems to be the nature of iAd's interstitials.

import UIKit
import iAd // Import iAd

class ViewController: UIViewController, ADInterstitialAdDelegate { // Include the delegate

    var iAdInterstitial = ADInterstitialAd() // Our ad
    var iAdInterstitialView = UIView() // View to present our ad in
    var adLoaded = false // Bool to keep track if an ad is loaded or not

    override func viewDidLoad() {
        super.viewDidLoad()
        setupAd()
    }

    func setupAd() {
        // Set presentation to manual so we can choose when to present the interstitial
        // Setting this will also fetch an interstitial ad for us
        self.interstitialPresentationPolicy = ADInterstitialPresentationPolicy.Manual
        iAdInterstitial.delegate = self // Set the delegate

        // Make our view the same size as the view we will be presenting in
        iAdInterstitialView.frame = self.view.bounds
    }

    func requestNewAd() {
        // This will fetch an ad for us
        ViewController.prepareInterstitialAds()
        println("Requesting new ad")
    }

    @IBAction func presentAdButton(sender: AnyObject) {
        if (adLoaded) {
            // We have an ad that is loaded so lets present it
            self.view.addSubview(iAdInterstitialView)
            iAdInterstitial.presentInView(iAdInterstitialView)
        }
        else {
            // No ad has been loaded
            println("Ad not loaded")
        }
    }

    func interstitialAdDidUnload(interstitialAd: ADInterstitialAd!) {
        // Kinda works as expected
        // Sometimes is called prematurely
        // Sometimes takes minutes after ad is dismissed to be called
        println("interstitialAdDidUnload")

        // Get new ad
        adLoaded = false
        iAdInterstitialView.removeFromSuperview()
        requestNewAd()
    }

    func interstitialAd(interstitialAd: ADInterstitialAd!, didFailWithError error: NSError!) {
        // Failed to load ad so lets try again
        println("didFailWithError: \(error)")
        requestNewAd()
    }

    func interstitialAdWillLoad(interstitialAd: ADInterstitialAd!) {
        // There is an ad and it has begun to download
        println("interstitialAdWillLoad")
    }

    func interstitialAdDidLoad(interstitialAd: ADInterstitialAd!) {
        // We got an ad
        println("interstitialAdDidLoad")
        adLoaded = true
    }

    func interstitialAdActionShouldBegin(interstitialAd: ADInterstitialAd!, willLeaveApplication willLeave: Bool) -> Bool {
        println("interstitialAdActionShouldBegin")
        return true;
    }

    func interstitialAdActionDidFinish(interstitialAd: ADInterstitialAd!) {
        // Done with this ad. Lets get a new one
        println("interstitialAdActionDidFinish")
        iAdInterstitialView.removeFromSuperview()
        adLoaded = false
        requestNewAd()
    }