How to: Jailbreak iPhone 3GS on iOS 4 with PwnageTool 4.0 [Mac]

iPhone Dev Team has Released the official PwnageTool 4 for Mac Users and compatible with the newly releases iOS 4 from Apple. Now you can Jailbreak your iPhone 3GS, iPhone 3G and iPod touch 2G (non-MC model only) on iOS 4 using the guide below..
Steps:
Step 1: Download and iTunes 9.2 from Here, and the Original iOS 4 from Here
Step 2: Start iTunes, and backup all your data by Right click on your iPhone and click on "Backup"
Step 3: Now, Download PwnageTool 4.0 from Here
Step 4: Launch PwnageTool 4.0 you have just Downloaded, Then choose your Device and Click on the blue arrow

Step 5: Now PwnageTool should detect the correct original firmware of your Device, Check on it and Click on the blue arrow

Step 6: A menu of several options will appear, Check on General and Choose your settings
Step 7: After choosing your Options, Check on Build and Hit the Blue arrow

Step 8: PwnageTool will ask you to Save Custom Firmware, Choose the place you want then Save it

Step 9: PwnageTool will now create the custom .ipsw file for your iPhone which will be jailbroken.

Step 10: Once the .ipsw file created, navigate to itunes, Click on iPhone on the left, then hold left “alt” button (“Shift” button on Windows) on the keyboard and then click on “Restore” then release the alt button
Step 11: iTunes now should ask you about the .ipsw file, head up it to the created custom firmware by PwnageTool

Step 12: Now, Sit back and let iTunes do it.. After several steps of installing the new firmware, Your device should be Jailbroken Successfully

Now, You will be Easily able to Unlock your iPhone 3GS on any Baseband Including 05.13.04 / 05.12.01 Using Ultrasn0w 0.93, Step by Step guide posted here.