Thats what I have found a few days before at this Forum.

What you need:
1. WinSCP - http://winscp.net/eng/download.php
2. puTTY - http://www.chiark.greenend.org.uk/~s.../download.html
3. bbupdater - http://**********.com/files/65139648...dows_.zip.html (Replace $ with letter s Unzip and extract "bbupdater", I don't know where else to get only the bbupdater)

What to do:
1. Install WinSCP
2. Check iPhone WiFi IP address -- Settings->WiFi->tap blue arrow->IP Address
2. Launch WinSCP - Enter IP Address in Host Name box, Username root Password alpine and uncheck "Allow SCP fallback". Click 'Yes' if a message window appears for the first connection attempt
3. WinSCP GUI will appear, your local PC directories will be shown on the left portion and iPhone directories will appear on the right. Browse to /usr/bin directory on iPhone if you already have that. If not make one by Right Click -> New or press F7 in the /usr directory
4. On the GUI, look for bbupdater you just downloaded, drag and drop it into iPhone's /usr/bin directory. MAKE SURE to set the permission to 0755!
5. Close WinSCP
6. Launch puTTY.exe
7. Enter the same IP Adress in Step 2 to the Host IP Name and click 'Yes' to the message for the first connection attempt
8. Enter root as login prompt and alpine as Password and you will see a '#' symbol
9. In the puTTY window, type: (to disable Comm Center)

launchctl unload -w /System/Library/LaunchDaemons/com.apple.CommCenter.plist

10. Nothing will happen but then type:

bbupdater -v

The following message will appear and you can now write down the bootloader version of your phone:

Resetting target...
pinging the baseband...
issuing +xgendata...
firmware: DEV_ICE_MODEM_04.01.13_G
eep version: EEP_VERSION:207
eep revision: EEP_REVISION:8
bootloader: BOOTLOADER_VERSION:3.9_M3S2

11. Finally type: (to enable Commcenter again)

launchctl load -w /System/Library/LaunchDaemons/com.apple.CommCenter.plist

12. Power cycle your phone and you are done!!