Alot of mobile sites are being put at m.domain.com. That is M as a third level domain inplace of your normal www.domian.com. Mobi is pretty much a nonstarter and few are using for anything except spam.
> iphone app
I wasn't referring to that. Unless you are a large site taking in well over six figures a year, a iphone app just wouldn't make econ sense unless you can produce a value add.
What you can do, is develop a smart phone friendly version of your site that will server all phones with browser and not just one os.