% cd /System/Library/SyncServices/MotorolaConduit.bundle
% cd Contents/Resources
% sudo emacs USBDevice.plist
and add, before the last tag set, the following entry:
<key>A835</key>
<dict>
<key>idProduct</key>
<integer>12290</integer>
<key>idVendor</key>
<integer>8888</integer>
</dict>
Now reboot and plug in your A835 with the USB Cable. iSync will find your mobile and you can sync it without problems.
[robg adds: I split the first command into a couple cds so that it fits width-wise on the site; obviously you can enter it as one long sudo emacs command. And I can't test this one, lacking such a device...]

