Well if u did an actual full sync then u should have a full backup of the phone. Now that your phone is on iOS 6, plug it in, go to itunes and on the left column, right click on your iphone and click on "restore from backup". U should see a list of backups with dates. Select the latest one and let the phone restore (15 min). U should get everything back as before (including in-app purchases and downloads. But of course, all of your jailbroken apps (i.e. paid apps that u installed for free) will not install because iOS 6 is not yet jailbroken