It sounds as if you misunderstand the process. If you are trying to use the old phone and want it to look like the new phone, then you need to do a backup of the new phone and restore the old phone to that backup. You cannot just connect and old phone and try and sync and expect it to take the new data. The differences in data between the two devices and iTunes could result in quite a mish mash of data. A sync does not take care putting the backup of the new phone to the old phone. It requires a restore. Go into iTunes and turn off the auto sync to start with, then after selecting the phone in the device pane, click on the Restore Backup button, choose the backup from the current phone.