As with all mobile devices, the iPhone's smaller screen and portability means that there are limitations in the physical size, processing power, and connectivity available. These limitations shouldn't be feared, instead they're great opportunities to refine your message and deliver the most relevant experience to your future customers.
Smaller screens means you need to make better use of the limited screen space available to you; for example, tappable areas need to consider the inconsistent accuracy of users' fingers. We need to make sure all tappable areas are at least 88px tall and wide, with sufficient space between each actionable element to prevent unintentional taps that are detrimental to the user experience.
Note
When designing your iAd banner, keep in mind that the bottom-right of the banner will be obscured by the iAd logo, so don't put any important information there.
It's important to remember that you shouldn't try...