Fuzzyband is the preferred application for downgrading your baseband since it does version checking, downgrades all versions of baseband from 2.30.03 to 4.26.08 (3.0 beta5), and it reports the current bootloader version on screen.
Press to launch Cydia from your SpringBoard.
Press to select the Sections tab at the bottom of the screen.
Press to select System from the list of sections
Press to select 3G Fuzzyband Downgrader from the list of packages
Press the Install button at the top right of the screen.
Press the Confirm button at the top right of the screen to begin installation.
Once installation has completed successfully press the large Return to Cydia button.
Press the Home button to return to your SpringBoard. Notice there is a new application icon titled Fuzzyband. Press to launch the application.
Immediately upon launching the application you will be shown a message stating that Fuzzyband is querying your modem.
Once it completes you will be displayed your Bootloader Version, your Baseband Version and your iPhone OS version.
If you have a bootloader version higher then 5.08 you will not be able to downgrade your baseband and a Not Supported message will be displayed.
If you have the 5.08 bootloader you will be able to downgrade from baseband 2.30 or higher. Press the Downgrade button to begin downgrading your baseband.
Once the downgrade has completed successfully you will be displayed a Done! message saying, "I Haz Downgrade!" and you will be on the 2.28 baseband.
***THANKS: to w1kedZ/DHowett for creating this utility