PwnageTool developed by the iPhone Dev Team is a nifty tool for iPhone users wishing to jailbreak their iDevice. 

This article will provide a step-by-step procedure for Mac users to jailbreak their iPhone 3G using the PwnageTool for iPhone OS 3.1.3. 

Some important points to note before we start:

• Please be forewarned that jailbreaking your iPhone may void your warranty and hence proceed only at your own risk. 
• This guide is only applicable for iPhone 3G users.
• Please take a backup of your iPhone, refer to this post for more details.
• After you have successfully jailbroken your iPhone, please checkout our article on tips to keep your iPhone secure and to change the password of your jailbroken iPhone.
• PwnageTool is only available for Mac users. Windows users who want to jailbreak their iPhone 3G can use Sn0wbreeze.     

Step 1: To start with, you will need to PwnageTool and the iPhone OS 3.1.3 firmware. You may download these by clicking here (PwnageTool 3.1.5, iPhone1,2_3.1.3_7E18_Restore.ipsw).

Step 2: Double click on the PwnageTool icon to launch the application. You will be presented with a Warning information. Click OK to proceed. On the top menu of the application, click on the 'Expert mode' icon (The option with the picture of Einstein on it).

Step 3: You are asked to select your iPhone model. Select iPhone 3GS from the list and click on the Blue arrow mark to proceed.

Step 5: You will now be taken to the "Browse for IPSW" page. If the application does not detect the ipsw file, click on the 'Browse for IPSW' link to select the firmware file that was downloaded in step 1. Once done, click on the blue arrow to proceed.

Step 6: The application will now display the firmware bundle customization screen. Click on the 'General' option and press the blue arrow to continue.

Step 4: Under the General settings, select the 'Activate the Phone' option if your iPhone is legitimately activated on an official carrier like the AT&T. Otherwise deselect the option. 

Step 5: Specify a Root Partition size of around 700 MB and press the blue arrow button to continue.

Step 6: Users are now taken to the Bootneuter page. However, this section is disabled for iPhone 3G users and so you may simply click on the blue arrow to proceed further.

Step 7: You are now displayed the 'Cydia Settings' tab. Click on the 'Download packages' tab and press the Refresh button to view the available packages. Checkmark the packages that you need (OpenSSH and OpenSSL) and press the blue arrow button.

Step 8: You will now see the 'Custom Packages Settings' menu. Skip this section and click on the blue arrow button.

Step 9: You can now choose a custom logo for your package. You can select one logo each for the Boot and Recovery modes. Remember that they need to be grayscale/RGB images under the dimension of 320×480. Once done, click on the blue arrow button.

Step 10: You will now be taken back to the firmware bundle customization page. Click on the 'Build' option and click on the blue arrow.

Step 11: Your custom .ipsw file is created. Save it on your desktop. It will take close to ten minutes for the process to be completed.

Step 12: You will now be prompted to enter your admin credentials. Once done, click on the 'NO' option in the dialog box that appears.

Step 13: The application will now instruct you to turn your device off. Ensure that the device is tethered and then switch off your iPhone.

Step 14: Follow the instructions offered on the screen. You will first be required to press the Home and Power buttons on your iPhone for ten seconds followed by pressing the Home button alone for 10 seconds.

Step 15: You can now unplug the iPhone from the USB. Restart your iPhone and plug the device back into the USB. Turn the device off when prompted.

Step 16: The device will now enter the DFU mode. When done correctly, PwnageTool will display a message telling your that it successfully entered DFU mode. iTunes will also pop-up. In iTunes, hold the Alt/Option button and click on the 'Restore' option. (This is a VERY IMPORTANT STEP as just pressing the "Restore" button will result in restoring your iPhone with the latest firmware which is firmware 3.1.2 currently, by holding down Alt/Option button, allows you choose the custom iPhone firmware file.)

Step 17: A dialog window will now open prompting you to select the .ipsw file. Select the .ipsw file that you just built and click 'Choose'.

Step 18: iTunes will now restore your iPhone's firmware. This will take close to 10 minutes. Once your iPhone 3G is restored, it will be jailbroken and updated with iPhone OS 3.1.3.

Step 19: The last step is to set up your iPhone 3G from a backup.

As always, don't forget to drop us a line to tell us how it goes.

[via iClarified]