title: Using iAd as default ad network, and AdMob if iAd fails
body: <p>I've built my app this way and everything seems to be working more or less. After hearing about the notoriously low iAd fill rate I decided that this would be the best method, but I tried googling it and i couldnt find record of anyone else implementing ads in their app like this.  Does this violate the TOS?</p>