I used this hint about the Motorola A1000 to get my new Panasonic X800 to work with iSync, with the knowlege that (1) iSync supports the X700, and (2) the X800 is almost identical to the X700, but in a prettier package.
Edit this file: /Applications -> iSync.app (control-click and choose Show Package Contents) -> Contents -> PlugIns -> ApplePhoneConduit.syncdevice -> Contents -> PlugIns -> PhoneModelsSync.phoneplugin -> Contents -> Resources -> MetaClasses.plist. Add this text to the file, right before the following line:
<key>com.panasonic.X700</key>
Re-pair your phone, and voila! If you're even more motivated, you can add your own icon, and replace the "PANX700.tiff" string with your new icon graphic.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050615125336114