Only yesterday I showed you the erase method to downgrade 04.12.02 to 04.10.01 iPhone 4 baseband but this method didn't work. However some of our readers immediately asked another question: "Is it true that you can disable the iOS 6 and iOS 6.1 baseband update?" Well, let's find answers on this question here. There is not a secret that everyone can use Redsn0w tool to upgrade iPhone to iOS 6 while preserving old baseband. Today we will try to disable the iOS 6.1 baseband update if you delete "psi_flash.fls" and "stack.fls" in the .bbwf file. According to iOS Hacker's Handbook:

For newer iPhones and the iPad 2, the baseband firmware can be directly extracted from the IPSW using unzip. Below you can see the ICE3 firmware is the version running on the X-Gold 61x in the iPhone 4, and the Trek file is used to upgrade the firmware running on the MDM6610 in the iPhone 4S. Baseband firmwares contained in the iPhone 4S 5.0.1 update $ unzip -l iPhone4,1_5.0.1_9A406_Restore.ipsw Firmware/[IT]\*bbfw Archive:  iPhone4,1_5.0.1_9A406_Restore.ipsw Length      Date   Time      Name --------     ----    ----    ---- 3815153   12-04-11 02:07   Firmware/ICE3_04.11.08_BOOT_02.13.Release.bbfw 11154725    12-04-11 02:07   Firmware/Trek-1.0.14.Release.bbfw --------                   ------- 14969878                   2 files The .bbfw files themselves are ZIP archives as well and contain the actual baseband firmware together with a number of loaders: $ unzip -l ICE3_04.11.08_BOOT_02.13.Release.bbfw Archive:  ICE3_04.11.08_BOOT_02.13.Release.bbfw Length      Date   Time      Name --------     ----    ----    ---- 72568   01-13-11 04:14   psi_ram.fls 64892   01-13-11 04:14   ebl.fls 7308368   12-04-11 02:07   stack.fls 40260   01-13-11 04:14   psi_flash.fls --------                   ------- 7486088                   4 files $ unzip -l Trek-1.0.14.Release.bbfw Archive:  Trek-1.0.14.Release.bbfw Length      Date   Time      Name --------     ----    ----    ---- 19599360    12-03-11 10:06   amss.mbn 451464   12-03-11 10:06   osbl.mbn 122464   12-03-11 10:06   dbl.mbn 122196   12-03-11 10:06   restoredbl.mbn --------                   ------- 20295484                   4 files Here we are only interested in the stack.fls for the X-Gold and in the amss.mbn for the MDM66x0 chipsets. All other files are loader files, which we don't investigate further; although these may in principle contain security-critical bugs — for instance, in the signature verification of the firmware, which would allow you to run different firmware on the phone and hence unlock it.

So, we can start but as in the case with previous guide about erase method you will need:

• Java must be installed.
• Read all notes carefully.
• This method is only for advanced users.
• For those who do not know how it works, it need not even try!

Update to iOS 6.1 / 6 Without Upgrading Baseband

Note: we don't recommend to perform steps below because it can harm your device. Note 2: there is now iOS 6.1 firmware for the time of writing this post but if it will work on iOS 6 it will work on iOS 6.1 as well. Step 1. Download iOS 6 firmware here. Step 2. Open it using WinRAR program. Step 3. Go to folder with downloaded firmware and delete:

psi_flash.fls

and

stack.fls

in the .bbwf file. Note: You can also extract to really be 100% sure the firmware file BBWF ending. Delete from the folder "firmware". Then zipping off everything again. Make it as ipsw file extension. Step 4. Now you need to enter DFU mode, not Pwned DFU. Step 5. Run iTunes and point it to iOS 6 with no BBFW file using Shift/Control button and clicking Update. If your are reading this post when iOS 6.1 is out then point to this new firmware. Step 6. If anything goes fine, you will end up with error 11. Step 7. To fix it open TinyUmbrella for iOS 6 / 6.1 and click on Exit Recovery. Note: Also you will probably get error 1004. In this case you will have to use TinyUmbrella and click "Kick Device Out of Recovery" Personally, I have deleted these files in the iOS 6 baseband firmware. But I can't be 100% sure that nothing will be updated. However the pwnage tool is simple and you do not get out of the recovery mode. You can try this method but it is on your own risk. ATTENTION As for me, the best way to keep iPhone unlock while upgrading to iOS 6.1 or iOS 6 is not baseband preservation. All you need to do is free your iPhone from carriers chains using IMEI unlocking service for AT&T. Or if you are not AT&T user you can try permanent iPhone unlock for almost any carrier around the world. It will give the possibility to update to iOS 6.1, 6 with baseband update and still be unlocked permanently.