If you are doing an iPhone restore and encounter error 1600 in your iTunes with message "The iPhone "iPhone" could not be restored. An unknown error occurred (1600).", heres what you can do.
Most likely, you are on iPhone DFU mode. Reboot your iPhone to normally by pressing Home + Power Button together for 10 seconds. Your iPhone should start to reboot normally. After booting up, try your custom restore again.
Good luck. ;)