Not many people can afford to own the expensive iPhone, and I am surely puzzled if this is something an iPhone lover would buy (I would rather burn the $$ on the AppStore).
Designers and luxury good makers have found iPhone to be a good playground. This lets them get some media buzz, and if some Apple fanatic lands, make some money as well.
However, a 24K gold iPhone is up on ebay for sale. Expected price is $1500.