Alas, I can tell that you are not currently using an iPhone or Touch. But...

Here's the basic code I'm using.

$browser = getenv("HTTP_USER_AGENT");
if (eregi('iPhone', $browser)) {
...
}

Where there are elipses (...) you do whatever you want -- the most likely best use being to point to an iPhone-friendly stylesheet. Then the question is, what IS an iPhone-friendly stylesheet? Digging a little deeper, what will iPhone users respond best to?

What I've learned thus far is:

• Use W3C Standards
• Separate content from look/feel/layout; use CSS for the latter
• Design for 320 x 480 pixels or vice versa
• Use columns and blocks
• But avoid wide columns
• Think 1996 for bandwidth and keep total file size very small (EDGE can be heart-breakingly slow)
• Use larger links, because a finger is not a mouse