Mactomster.de (a German website) has developed an iSync plugin for synchronizing your Nokia S60 3rd Edition device with Apple Mac OS 10. This plug-in requires Mac OS X 10.4.7 9 or later (works with MacIntels too, the site claims) and iSync v2 or 3. This plugin supports Nokia E50, E60, E61, E70, N71, N72, N73, N80, N91, N92, N93, 3250, 5500, 6131, 6233 and 6234.

Original site here and the German translation here

Update: Nokia has released their own official plug-ins for Apple iSync to synchronize calendar and contacts between Nokia S60 2nd and 3rd Edition mobiles with Mac OSX