If you need to redirect the user (presumably because your layout cannot simply be shrunk down to fit a tiny screen) then you can write (or download an off-the-shelf) PHP user agent detection script. click here for one example that is supposed to be pretty up to scratch. If you don't need the redirect, use media type statements in your style sheet links. Please keep in mind the fact that user agent reporting is flexible and therefore its detection can be patchy. For that reason, I avoid it.