I read the tutorials for web applications and the special rules you can put into style sheets. Are folks finding they can just tweak their style sheets to serve up content to iPhones or do they deliver custom iPhone specific pages? would you bother with this if you were going to create a specific page anyway for mobile users ? (even if targetted at iphone/smartphone users only)
Any advice would be appreciated
You can indeed trap the incoming request, find out it's an iPhone/SmartPhone/Mobile device, and serve other CSS files accordingly.
I would not define extra mobile-specific rules/selectors in a CSS file, but serve another, trimmed down and prepared CSS file.
But that will only alter the way your HTML looks, and not what you serve to the client, in this case a mobile device.
Mostly, we serve other HTML as well, as you have to take bandwidth into account. We serve 'less' HTML, i.e. a trimmed down version,of the original page, to mobile devices.
Look at what Twitter does for mobile devices: http://m.twitter.com/login They not only serve another look, they also serve other HTML and less functionality (or less functionality on one page).