As I pointed out in a post a few days ago, testing handheld CSS is problematic. Here are a few of the resources that are available.
Opera’s View > Small Screen feature comes close to emulating some handhelds, and will display a page with handheld CSS accordingly. It also does a decent job of displaying a page with no handheld CSS as it would look on a handheld. Even more helpful is the Opera Mini Simulator an online simulator that looks like a phone.
Online simulators are scarce for individual mobile devices. Most manufacturers have some help in their support pages and many offer a downloadable emulator, such as this one from BlackBerry.