How do I detect an iPhone user on my website?
Don't.

The only reasons to ever have a separate mobile site are cheapness and laziness.

The right approach is to have your visitors all get the same content; the only thing that should change how that content is styled—and doing that doesn't need a separate site, or even a special page.

If your next question is "Can iWeb do that?," the answer is that I doubt it, because iWeb just isn't meant to be a professional web development tool. If you're looking for an alternative, I recommend TextWrangler—it's both better and cheaper.



References:1


How to Make Your Website Mobile Today, InfoWorld, 20 September 2010
Mobilizing Your Web Site, Users Conference session at Macworld Expo 2011, 28 January 2011


1 Yes, they're both me.