First of all, HUGE thanks to TA_Mobile and IMTH for getting us the secpack from 1.1.3 Also, thanks to psp_sully for giving me a 1.1.2 OTB phone to play with. Without them there would be no unlock, and no blog post.
YOU VERY WELL MAY BRICK YOUR PHONE WITH THIS. Be careful. I have done it sucessfully on two phones, and have never bricked an iPhone in my life.
So lets get down to business. It is a hardware method to downgrade the bootloader, and I am assuming you are familiar with the old hardware method, so I won't repeat steps. You need to have a 1.1.2 4.6 phone for this to work. If you upgraded to 1.1.3, have fun waiting for 1.1.4!