Before you begin please have MobileTerminal and OpenSSH installed from Cydia. You can find MobileTerminal in the Terminal Support section of Cydia. For instructions on how to install an application from Cydia you can use this tutorial.
Download BBUpdaterExtreme from here and save it to your desktop.
Launch the Terminal application from Applications:Utilities.
Make sure you iPhone is connected to the same wireless network as your computer and determine its IP Address using these instructions.
Enter the following command into the Terminal window replacing the IP Address below with the one for your iPhone.
scp ~/Desktop/BBUpdaterExtreme email@example.com:/bin/BBUpdaterExtreme
You will be asked for your password. Enter alpine as the password.
Input the following command to ssh into your iPhone.
You will asked for your password. Enter alpine as the password.
Input the following commands into the Terminal window
chmod 755 BBUpdaterExtreme
launchctl unload /System/Library/LaunchDaemons/com.apple.CommCenter.plist
Your iPhone will now loose its network connections. Launch Mobile Terminal from the iPhone SpringBoard.
Type su into the terminal window. When asked for a password input alpine as the password.
Now input BBUpdaterExtreme queryversion to get the bootloader version of your iPhone. It will look something like Boot Loader Version: ICE2_BOOT_05.08_G2M3S2
NOTES: You will need to restart your iPhone to regain network connectivity. You could also type launchctl load /System/Library/LaunchDaemons/com.apple.CommCenter.plist into the terminal window.