The iPhone, by most accounts has been a huge success, created unparalleled gadget-envy and has signaled a shift in the US mobile handset market. I've seen a lot of companies riding this wave of popularity and, subsequently, have released exclusive iPhone sites (Six Apart and Facebook to name two). These sites are physically formatted for the device, use specific technology and won't work on most other handsets.
From a mobile marketing strategy view I think this begs the question, should you design a site just for the iPhone? My answer is "it depends". Unless you work for Apple, designing for the iPhone should be part of a larger mobile strategy. Focusing on the iPhone alone isn't an effective way to move in the mobile space. Let's put this in perspective.
Here are the global numbers for some of the larger mobile device manufacturers for their last reported fiscal quarter.
Apple | 1 million units reported
Nokia | 100.5 million units
Samsung | 37.4 million units
Motorola | 35.5 million units
Sony Ericsson | 24.9 million units
LG | 19.1 million units
Blackberry | 2.4 million units
That being said, designing an iPhone-only version of a product or site is a way to reach the young, hip, early adopters that the product attracts. More and more phones will start to shift to model themselves after the iPhone, but that could take a couple of years to come to market in mass. In the meantime, the iPhone can be a great addition to the mobile mix, but don't put all of your eggs in that iBasket.