Note: if you are having any difficulty and / or want online virtual assistance service in ulocking / jailbreaking your Iphone / iPod 3G / 3Gs click here: http://nabtron.com/online-iphone-ios-4-0-jailbreak-and-unlock-service/
Note 2: Click here for unlocking iOS 4.0.1 click here
iPhone Dev team has finally released an updated version of ultrasn0w compatible with iOS 4.0. the latest version of 
To unlock your iPhone 3g / 3Gs to allow it to use any carrier network you want, first you need to jailbreak it.Follow this tutorial on how to jailbreak the iPhone 3G/ iPhone 3Gs on iOS firmware 4.0 and then continue with this tutorial to unlock it.
How to Unlock iPhone 3G/3GS any baseband (05.13.04 to 04.26.08) on iOS4 using Ultrasn0w 0.93
Once you have jailbroken your iPhone 3G / 3Gs, now its time to unlock it too. The unlocking of the new iOS 4.0 is similar to previous versions of the apple iPhone firmwares. We need to install ultrasn0w via cydia to unlock it. Follow these steps to unlock your iPhone 3G / iPhone 3Gs with ultrasn0w on iOS 4.0 and latest / any baseband.
1. Jailbreak your iPhone
As mentioned earlier, make sure you have upgraded your iOS to 4.0 and jailbroken it.
2. Add source to Cydia
Run the Cydia app in your iPhone and:
- Goto Manage option at the bottom of the Cydia app screen.
- Add sources by going to Sources.
- Press Edit to add new source and add this source to your Cydia sources list:
http://ios4.ultrasn0w.org
- wait for Cydia to update the sources, this may take some time.
3. Install ultrasn0w 0.93
After the update is over search and install ultrasn0w 0.93 from Cydia.
Installing it will unlock your iPhone 3G/3GS on iOS4.
4. Restart
Once the above steps are complete, just restart your iPhone 3G / iPhone 3Gs and ladies and gentle man now you have the latest version 4.0 of iOS successfully jailbroken and undoubtedly unlocked, giving you the power to use your apple device with any cellular network and data provider carrier now!
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