Open a terminal window. Go to the directory /System -> Library -> SyncServices -> MotorolaConduit.bundle -> Contents -> MacOS. Use emacs or any binary-capable editor to modify the executable file MotorolaConduit. Assuming you're using emacs, type Control-S followed by C330 to find the string "C330." Modify the string into C350. Now type Control-X followed by Control-S to save the file and exit. Make sure you have not modified any other byte in the file.
Go into /System -> Library -> SyncServices -> MotorolaConduit.bundle -> Contents -> Resources and copy C330.tiff to C350.tiff. Edit the file USBDevice.plist, and go to the line that reads:
<key>C330_CDMA</key>
and change it to read:
<key>C330_CDMA,C350</key>
Then launch iSync and in the Devices menu do Add Device ... I just synched my C350 with iCal, so I know this works.

