To follow this tutorial you must have 1.1.4 firmware installed on your iPhone. If you accidentally downgraded to 2.0 then use this tutorial to downgrade to 1.1.4.
Download KiPhone from here to your desktop: Mac, Windows
Double click the downloaded zip file to extract its contents.
Double click the extracted file (ZiPhoneOSX patched by kIREmK 04.05.04_G [En]) to launch the application.
Once the application has launched make sure the BL 3.9 & 4.6 tab is selected. Also make sure the Baseband downgrading checkbox is selected.
Connect your iPhone to the computer and click the Start button. ZiPhone will put your iPhone into recovery mode and you will be informed that the process will take 2 mins and 30 seconds.
If you are a windows user then simply check off Downgrade Baseband and Debug Boot and click the Start button.
Once the process is complete you will be informed that it completed successfully. You now have downgraded your Baseband to 04.04.05_G!