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 
Ultrasn0w 0.93 is available in cydia and is capable of unlocking apple devices such as iPhone 3G, iPhone 3Gs with any baseband (uptil 22nd june, 2010 – including 04.26.08, 05.11.07, 05.12.01 and 5.13.04) on iOS 4.0.
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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x-cellent ! i was waiting for this a couple weeks ! great job dev-team !! now i have jailbroken iPhone 3G with iOS4 and because i dont have a wi-fi connection at home i gotta go to the internet cafe to download ultrasn0w ! I can`t wait !!!!
Glad to know that :) enjoy!
HELPPPPP
I have iphone 3g 05.13.04 baseband FW 3.1.3, installed cydia and ultrasn0w 1.1-1. NO SIGNAL, NO SERVICE.
Tried:
hard reset-15 times
RESET:-20 times
REBOOT:20 times
Restore : 10 times
network reset: 100 times
reset all setting: 50 times.
Sim Pop in-out: 10 times
Change different carrier sim:20 times
install ultrasn0w .093: 5 times
install ultrasn0w 1.0-1 :5 times
install ultrasn0w 1.1-1: 10 times.
cydia fully updated.
I got full network in all carrier. so no issue of low signal. also wifi is working fine
STILL NO LUCK. NO signal in my iphone. Now iphone becomes ipod 8gb.Help me guys.
make sure:
1. wifi is working
2. bluetooth is working
and also make sure:
by inserting the At & T sim, the signals arrive or not