iOS 4 was released earlier today and the iPhone Dev Team was quick enough to release an ultrasn0w unlock for it. Thanks to the unlock, and the recently released redsn0w 0.9.5 beta 5, you can install, jailbreak and unlock iOS 4 on your iPhone 3G. Make sure you follow the instructions correctly.

1. Download iOS 4 for your iPhone 3G. Place it on your desktop for easy access.
2. Download redsn0w 0.9.5b5-4 [links at the end]. It’s available for both Mac and Windows.
3. Download and install iTunes 9.2
4. Now connect your iPhone 3G to your computer and using iTunes, upgrade to iOS 4. Do this the official way as described here.
5. Now that you have iOS 4 final build on your iPhone 3G, you’ll have to jailbreak it by using the iOS 4 with redsn0w 0.9.5 Beta 5. Click browse and point it to iOS 4 firmware and follow the instructions on screen. Remember to enable battery percentage, wallpapers and multitasking. 
6. [Vista users might needto run redsn0w as administrator]
7. Once you’re done and the iPhone reboots, you should have a jailbroken iPhone 3G.
8. Now go to Cydia and add the following repo http://repo666.ultrasn0w.com. Check here for how to do this. Search for ultrasn0w 0.9.3 and install it and reboot again. Your iPhone 3G is now carrier unlocked. Also remember to add this repo to Cydia http://apt.saurik.com/cydia-3.7.

Download redsn0w 0.9.5b5-4

• Mac OSX (x86)
• Windows

To fix and enable Push Notifications on your hacktivated/unlocked iPhone, follow this guide.

UPDATE: the guide has been updated to reflect the recent release of redsn0w 0.9.5 beta 5-4 which fixes the iBooks issue that users were reporting.

If you face any issues, don’t hesitate to ask us in the comments. We’ll be glad to help!