If you are mac user then you have quite few options like Redsn0w 0.9.5 Beta 5 & Pwnagetool 4.0.1 to jailbreak iOS 4.0 on iPhone 3GS & iPhone 3G. Redsn0w 0.9.5 Beta 5 is also available for Windows but it can’t jailbreak iPhone 3GS 4.0 and you have to rely on custom firmware for iOS 4.0.
Well now with release of Sn0wbreeze 1.6.1 you don’t have to, Sn0wbreeze 1.6.1 is like Pwnagetool 4.0.1 for Mac. Using sn0wbreeze 1.6.1 you can create custom firmware on Windows and jailbreak your iPhone3G/ 3GS 4.0 (old boorom) & iPod Touch 2G 4.0 iOS.
The options provided by sn0wbreeze 1.6.1 are similar to Pwnagetool, you can activate multitasking, custom recovery logo, unlock etc. Once again we are back with complete step by step guide to jailbreak iPhone 3G & iPhone 3GS 4.0 iOS using Sn0wbreeze 1.6.1 on Windows (custom firmware method).
How to Jailbreak iOS 4.0 with Sn0wbreeze 1.6.1 on Windows
4. Put everything in one folder and name is “ios4.0”
5. Now Start sn0wbreeze 1.6.1 and click “blue arrow” and select “simple mode” and continue.
If you select expert mode you will be able to get thru many options include ability to install custom boot/recovery logo etc.
6. Now browse and select iOS 4.0 ipsw file downloaded in step 1 for your respective device.
7. Sn0wbreeze 1.6.1 will process 4.0 ipsw and will verify select ipsw file.
8. Now click on Blue arrow icon and wait for Sn0wbreeze 1.6.1 to complete processing.
9. Click yes/ no if you want to activate iPhone.
10. Let Sn0wbreeze 1.6.1 to complete rest of its process
11. Sn0wbreeze 1.6.1 will show the message once it has done, now select whether your iPhone 3G is jailbroken or not.
12. Now connect your iPhone 3G and enter in Recovery mode after that launch itunes and hold down shit while clicking the restore button on iTunes.
13. Now let iTunes complete installing iOS 4.0 custom firmware on your iPhone 3G/3GS.
Once your iPhone restarts, the jailbreak process will complete, now enjoy your jailbroken iPhone 3G/3GS 4.0.
Unlock iOS 4.0