If you own an iPhone 3G with 05.08 bootloader, you can now unlock your jailbroken iPhone 3G running iPhone OS 4. Once you jailbreak iPhone 3G on OS 4 using Redsn0w 0.9.5, you can install Cydia repository and access apps for jailbroken iPhone.
The trick is to downgrade baseband of your iPhone 3G 4.0 to unlockable version like 04.26.08 which can be unlocked using Ultrasn0w 0.92. Fuzzyband Downgrader on Cydia can now downgrade iPhone OS 4 bootloader 05.13.03 provided you have 05.08 bootloader on iPhone 3G.
Below is the step0by-step guide to unlock iPhone 3G 4.0 using ultrasn0w 0.92
Unlock iPhone OS 4.0 with Ultrasn0w 0.92
Step1: Jailbreak your iPhone 3G using Redsn0w 0.9.5.
Step2: After jailbreaking your iPhone, Downgrade your iPhone OS 4 Baseband 05.13.03 using Fuzzyband.
Step3: Once downgrading is complete, Go to “Cydia” and tap on “Manage” tab at the bottom. (Disable 3G if you are on official carrier).
Step4: Tap on “Edit” and then tap on “Add” button. You will prompt to enter a url Source. Type “http://repo666.ultrasn0w.com” and click on “Add Source“.
Step5: After adding repository search for “Ultrasn0w” in Cydia and install this.
Step6: When installation is complete, just restart your iPhone.
You should now have an unlocked iPhone 3G!
Disclaimer: This guide is for testing & educational purposes only. We are not responsible for any loss of important data or malfunctioning of your iPhone.