1. You will need to have a jailbroken iPhone with Cydia installed. If you do not know how to jailbreak your device there are other guides that will help you to do so. You will only be able to downgrade the baseband on a 3G iphone with a bootloader version of 5.08
2. Select Cydia from your home screen.
3. Once Cydia is open, click “Search” in the bottom right.
4. Click on the search tool bar to begin typing
5. Type in “Fuzzyband” without the quotes and then hit search.
6. Select Fuzzyband and the download page will open.
7. Click the “Install” button in the upper right.
8. You will be directed to the next installation screen. From there you will need to hit “Confirm” in the upper right.
Notifier will begin to install
9. When the install is complete press the home button on your phone, browse for the Fuzzyband app. It will be labeled “Fuzzyband” and open it
10. Once open, Fuzzyband will query your modem.
11. When it says “Ready to Downgrade” hit the downgrade button. It will then say Downgrading. When the downgrade has completed it will say “Done” and “I HAZ DOWNGRADE” in green.
You have now downgraded your baseband and are ready for yellowsn0w or ultrasn0w