iOS 4.0.1 has been released for iPhones only (iphone 4, iPhone 3G and iPhone 3GS) but only iPhone 3G can be jailbroken with Redsnow 0.9.5. The users of iPhone 4 and iPhone 3GS will have to wait for new/update jailbreak tool. Again, this guide is only for iPhone 3G and don’t try to use it on other idevices.
Here is the step by step procedure to jailbreak iOS 4.0.1 on iPhone 3G using Redsn0w 0.9.5 beta 5 – 5 (all the download links are at the end of this post):
Step 1: Download iOS 4.0.1 for iPhone 3G.
Step 2: Download iOS 4.0 final version for iPhone 3G.
Step 3: Launch the iTunes 9.2 and update your iPhone 3G to iOS 4.0.1.
Step 4: Now start Redsnow 0.9.2 beta 5-5 and point it to iOS 4.1 ( Note it is firmware 4.0 and not iOS 4.0.1 in this step).
Step 5: In this step select Install Cydia and other options like multitasking and homescreen wallpapers if you want.
Step 6: Make sure your iPhone is switched off and connected to the PC.
Step 7: At this stage you will need to put your phone in DFU mode. To do this hold “Power” button and then while holding the “Power” button, you will now have to hold “Home” button too for about 10 seconds. Now after few seconds release “Power” button but keep holding “Home” button until installation begins(about 330 seconds).
Step 8: Let the Redsn0w to complete the jailbreak process.
Step 9: After the update process is complete, your phone will restart automatically. At this stage the Cydia icon will be blank. Go to the Sources panel and add http://apt.saurik.com/cydia-3.7 repo.
Step 10: Restart your iPhone and enjoy the jailbroken iPhone 3G on iOS 4.0.1.