We are aware of several of our users with the Samsung Galaxy S3 having issues with USB syncing on a Mac. Starting with iSyncr Desktop version 3.1.5, we think we have removed most, in not all, of these issues. Please make sure you are using "Media Device" (MTP) mode on your S3. Using Camera (PTP) mode is no longer recommended.

At this point, iSyncr should recognize your S3 and allow you to sync your media to the device. We would love it if you would drop us a line at [email protected] and let us know if you run into any issues.