It's a shame you didn't check for iSync compatibility on Apple's
Official iSync Supported Devices page before
buying the phone. Could've saved yourself some hassle...
No plugins are available for the Samsung U600 currently, and its possible there won't be until another iSync update, as the U600 works differently to the supported D600 and D900.
In addition to those on Apple's page, you can also add the phones from
here and
here.
Personally, for the best syncing experience I would recommend a Sony Ericsson model.