cash edit: All you OSX guys out there I have written a nice guide for you, it takes a little time but i tried to be as detailed as possible.
Click here for the Downgrade from 1.1.1 to 1.0.2 complete guide including baseband via osx
Revan has made the windows guide click here
All right! If any of you have "bricked" iPhones from upgrading unlocked iPhone's to 1.1.1, you are now able to downgrade without paying a dime!
The guys over at RDGaccess.com have put together a guide on how to do it, here it is:
"UNBRICKING 1.1.1 UPGRADE
0. Download firmware 1.0.2 from apple: http://appldnld.apple.com.edgesuite....8_Restore.ipsw
1. rename it to iPhone1,1_1.0.2_1C28_Restore.zip and unpack.
2. extract the ramdisk file from it by typing
dd if=694-5259-38.dmg of=ramdisk.dmg bs=512 skip=4
3. mount the ramdisk by doubleclicking it (on mac). On windows use some HFS tools to peek inside it or get the files from someone who extracted it already.
4. Put your phone into DFU mode and do option-restore in iTunes. This will reflash everything to 1.0.2. You will get an error at the end because it couldnt reflash the baseband. You will end up with a yellow triangle.
5. Quit iTunes, launch iNdependence and quit it again, relaunch iTunes. Press the power button on the phone for 3-4 seconds. After like 10 seconds you end up on the activation screen.
6. Complete the Downgrade by Jailbreaking / Activating, Installing SSh on to the phone etc. There are tons of wiki's about that so I won't repeat. (probably also true for step 4,5)
7. Extract the baseband firmware and EEPROM files of 3.14 from the ramdisk of firmware 1.0.2. The files are named ICE03.14.08_G.eep and ICE03.14.08_G.fls and are located under /usr/local/standalone/firmware.
8. Get the Secpack of baseband firmware 4.0. Its at the bottom of this post.
9. Download ieraser2 from http://www.fink.org/ieraser/ or from Geohot's blog.
10. Install all the tools on to the phone (i use the location /usr/local/bin)needed to get ssh access to the 1.0.2 firmware phone and upload ieraser2, the secpack, the firmware 3.14's FLS and EEP file and anySIM 1.0.2.
11. ssh to the phone. Stop CommCenter? by typing:
launchctl remove com.apple.CommCenter?
12. run bbupdater -v. it will tell you you run version 4.01 of the baseband.
(bbupdater is a tool by apple which is also on the ramdisk)
13. run ieraser2. This will WIPE your baseband, given a file "secpack" is in the same directory and this is a version 4 secpack.
14. run " bbupdater -v " again. it will not find any firmware now. 15. run " bbupdater -e ICE03.14.08_G.eep -f ICE03.14.08_G.fls " 16. run " bbupdater -v " it will tell you you run version 3.14 At this point in time you will still have a IMEI number starting with 004999... and its not of use yet. So still bricked but at least downgraded to version 3.14.
17. run anySIM Version 1.0.2 (note that older versions might not be good here as 1.0.2 has a lot of fixes for this kind of stuff).
Now you have a unlocked 3.14 baseband with IMEI being your original one! Congratulations you now fully recovered from your update 1.1.1 and are back to 1.0.2.
If you want to return to virgin state again you can stop the commcenter again and repeat " bbupdater -e ICE03.14.08_G.eep -f ICE03.14.08_G.fls " again to reflash the "locked" version of the baseband. "
All files needed are here