The supported device list contains a list of devices that Apple claims are explicitly compatible with iSync out of the box, subject to the limitations outlined in the footnotes at the bottom of the page [the ones that apparently almost no one ever reads] and the general rule that carriers may not support certain features [say, Bluetooth or USB] and may not support certain functions [say, calendar synchronization] with a supported device.
Manufacturers like Audiovox, LG, Samsung and Sharp are not supported, unless they run an OS listed below, instead of their proprietary operating systems. If a device is not manufactured by Motorola, Nokia, Panasonic, Seimens, Sendo or SONY Ericsson, it is generally
not supported, unless it uses…
• the Blackberry OS [which requires third-party software]
• the danger HipTop OS [which requires third-party software]
• the Palm OS [which is is supported but performs better with third-party software]
• the Windows Mobile OS [which requires third-party software*]
*Windows Mobile 5 device support is not yet available in release software.
…or, an iSync-compatible plug-in has been written to extend support to a specific device or family of devices.
Julian referred you to a site where he has made a number of plug-ins available for various mobile handsets. Nova Media also sells a low cost package of plug-ins providing support for various handsets.
http://www.novamedia.de/sync/index.html
Others have built single-use plug ins with various degrees of success, which you can find using tools like Google.
The bottom line: if you are going to vary from the iSync Supported Device list, you have to do some relatively extensive research, including searching these forums for your specific device, to determine if it can be supported. Many plug-ins are intended only to work with iSync 2.2, so Mac OS X 10.4.6 is a requirement in most cases.