After the successful unlock of the iPhone 3G with 2.1 firmware months back, now after the release of 3.0 firmware from Apple, i unlocked the iPhone 3G with 3.0 firmware using 2 tools released by the iPhone Dev Team. They are redsn0w and ultrasn0w.

I first tried to jailbreak the iPhone 3G with Pwnagetool but it did not take me correctly into the DFU mode, and gave problems but the redsn0w tool for mac was just awesome. Worked for me easily and jailbroke the phone in just a few minutes.
Here is how –

Download redsn0w for Mac here.
Download redsn0w for Windows here.
Install redsn0w and open the application. Then you would be taken through many steps where the first is to download iphone 3.0 firmware(not through iTunes) from alternative links and locate the firmware file to start the jailbreak process.
Then it goes through several processes like processing and identifying the firmware, installing it, patching kernels. Then you need to enter the DFU mode by –

• Switching off the iPhone 3G
• Holding the Power and Home key for 10 seconds together
• Release the Power button and keep holding the Home button until the next step starts automatically

You then need to select which app, either Cydia or Icy to install for 3rd party apps in the iPhone. Better select Cydia as its easy to use and in the tutorial below i have included steps on how to install Ultrasn0w through Cydia.
After this, the jailbreaking process is done with a few processes in the iPhone finish. Then you need to unlock the iPhone for all the networks, which can be done through the installed Cydia or Icy app.

Unlocking the iPhone 3G –
After the phone restarts, open the Cydia app and wait till it loads completely, should take a minute for everything to load.
Then go to Manage tab > Sources > and then add the following source by hitting “Edit” –
http://repo666.ultrasn0w.com
(This is the repo URL that helps you download and install the Ultrasn0w unlock tool in your phone)

Open that package, and you would see the Ultrasn0w tool package with the details. Download and install it.
Here are a few steps that would occur in the iPhone 3G as you see in the screenshots –

Then, follow these steps as i did in my iPhone 3G to unlock it. You too do the same –
After installing the Ultrasn0w, restart the iPhone. Then go to Settings > General > Reset > Reset Network Settings and the phone restarts.
Then go to Airplane mode, switch it on and off once. Then go to the main screen and wait for a couple of minutes and the signals would appear with your network name on the right to it.
This is the proof for the unlocked iPhone 3G with 3.0 firmware.

—

The unlock process was done in the same way as shown in the screenshots, and was done with a Mac OS X 10.5.7 using iPhone 3G and firmware 3.0. Unlock the phone with your own risk and do post any questions in comments. I will soon post a tutorial on how to jailbreak the 3.0 firmware with Pwnagetool if it lets me do that perfectly. And i have not unlocked an iPhone till today using a Windows computer, so not sure if the same tricks apply or not.