The Process (1.1.2 without OktoPrep and 1.1.2 Brand New OTB):
Step 1: If you are on this step, you have iPhone firmware 1.1.2 and did not install OktoPrep when on 1.1.1. You will need all of the downloads provided above, please download them now. Enter recovery mode on your iPhone by holding the power and home buttons until the "connect to iTunes" picture appeared. Once iTunes recognizes your iPhone, shift-click on "Restore" and navigate to your 1.1.1 Firmware. Allow iTunes to downgrade your 1.1.2 firmware to 1.1.1. When finished iTunes should give you error #1015.
Step 2: If you are on this step, you downgraded your iPhone to 1.1.1 and got error #1015. Open iBrickr and it should give you the option to boot the phone or to "Begin Downgrade to Firmware 1.0.2". Click on Begin Downgrade to Firmware 1.0.2 and follow the instructions provided (instead of going to the iBrickr folder for 1.0.2.ipsw, go to where you manually downloaded the firmware). After following iBrickr's instructions, activate your 1.0.2 iPhone with iTunes.
Step 3: If you are on this step you have an activated iPhone running firmware 1.0.2. Open iBrickr and click on Applications. Install PXL using iBrickr's instructions and install BSD Subsystem and OpenSSH (in that order).
Step 4: If you are on this step you have an activated iPhone running firmware 1.0.2 with OpenSSH installed. Open winscp405.exe (referred to as WinSCP from now on). For Host Name: Enter your current wifi IP address on my iPhone (check this by going to Settings > Wi-Fi > and clicking the blue arrow next to your SSID), Port number: 22, User Name: root, Password: dottie, Private key file: Leave blank, file protocol: SCP. Hit Save... and save the profile as iPhone (Hit yes if it asks you if you're sure you want to save a password). Now double-click on your new iPhone profile and allow up to a minute for your Host Keys to be generated (click yes when it asks you if you want to allow the Host Keys to be generated).
Step 5: If you are on this step you have an activated iPhone running firmware 1.0.2 and should be attached to your iPhone through WinSCP. Navigate to the /usr/bin folder on your iPhone and drag and drop the following folders from the Downgrade Pack to the /usr/bin folder on the iPhone:
ICE03.14.08_G.eep
ICE03.14.08_G.fls
iEraser
bbupdater
secpack
secpack.bin
After the transfer completes, exit out of WinSCP.
Step 6: If you are on this step you have an activated iPhone running firmware 1.0.2 with extra files in the usr/bin directory. Double-click on Putty.exe and use the same settings and password you used in WinSCP to login. (NOTE: when you type in the password, nothing will appear. Just type normally and hit enter when you are done typing dottie and everything will be fine). Type in the following hitting enter after each line:
launchctl
unload /System/Library/LaunchDaemons/com.apple.CommCenter.plist
exit (without this you will still be in launchctl and it will not recognize the command cd)
cd /usr/bin
chmod +x iEraser
chmod +x bbupdater
iEraser
bbupdater -v
The last command issued returned "baseband unresponsive to pinging". THIS IS GOOD! Now type in the following and hit enter:
bbupdater -f *.fls -e *.eep (the _'s are spaces: bbupdater_-f_*.fls_-e_*.eep)
After this process ends, backspace the text "PuTTy" that was left behind and issue this command:
bbupdater -v
This returns a slew of data which (roughly translated) means...SUCCESS!
Step 7: f you are on this step you have an activated iPhone running firmware 1.0.2 and have flashed the baseband. Back in iTunes, shift-click "Update" and navigate to your 1.1.1 firmware. Allow iTunes to update your iPhone to firmware 1.1.1 and then activate your iPhone using iTunes.
Step 8: f you are on this step you have an activated iPhone running firmware 1.1.1. Visit
www.jailbreakme.com URL on your iPhone. Click "Install AppSnapp". Your iPhone will navigate to another page and briefly show a blue square in the upper corner before Safari crashes. At this point a status HUD should pop-up and display the status of the jailbreak. If you do not see this status HUD, go back to
www.jailbreakme.com and try it again. After a successful jailbreak, your iPhone will soft-restart and you will see Installer.app on your homescreen. At this point I find it's best to do a manual restart (hold the power button until the "slide to power off" slider appears. Slide it off, then hold the power button until the iPhone starts back up). This step is optional though.
Step 9: If you are on this step, you have a jailbroken (if you have Installer.app, you are jailbroken) iPhone running 1.1.1 firmware. Click on Installer on you iPhone homescreen and allow it to check and refresh your sources. If necessary, update Installer (you will see an Installer update in the update tab in Installer if this is necessary). Under the Install tab, navigate to Tweaks (1.1.1) > OktoPrep and download OktoPrep. After the download, click the home button and allow the iPhone to soft-restart. Back in iTunes, shift-click on "Upgrade" (NOT RESTORE!) and navigate to your 1.1.2 Firmware (download here). If iTunes is already prompting you to upgrade to 1.1.2 it is not necessary to shift-click...simply click "Upgrade" and allow your iPhone to be upgraded (NOTE: if you do this, iTunes will automatically download the firmware taking around 5 mins at broadband speeds). Activate your iPhone through iTunes.
Step 10: If you are on this step, you have an activated iPhone running firmware 1.1.2 and had installed OktoPrep on 1.1.1 before upgrading. Close out of iTunes. Unzip and open the folder containing the 1.1.2 Jailbreak (download here). Double-click on windows.bat and hit enter when Command Prompt pops up. A Java window will pop up (I would suggest to check "Install SSH" but that's up to you). Click Jailbreak! A progress bar will pop up and Command Prompt will start displaying code. Let the program run (it should take under 10 minutes). After it's finished it will say "Done! Reboot your device (it will automatically reboot once after you do so)". And Voila! JAILBROKEN
http://www.modmyi.com/forums/showthread.php?t=15669&highlight=downgrade