With television and radio advertising, we're unsure about how engaged a viewer or listener is with our campaign; their attention could be (and often is) elsewhere. With iAd, we're almost guaranteed the user is immersed with our content, as they've opted to interact with it. This makes the cost per engagement with iAd more valuable. Typically, you'll find that you pay more for advertisements that target more popular demographics, but how this is measured and charged to you depends on the pricing model used.
Mobile advertising follows an advertising model similar to the Internet channels that you may be familiar with. If you aren't, or want a refresher, we'll take a look at the current models and a world of acronyms.