As you may already know, Redsn0w can jailbreak iPhone 4 and iPhone 3GS on the latest iOS 5 firmware. This is a tethered jailbreak for both the devices. The only exception is iPhone 3GS old bootrom, for which the jailbreak is untethered.
WARNING for iPhone unlockers: You should stay away from iOS 5 update as this will update their baseband and result in loss of unlock. You should also stay using Redsn0w in the regular way to jailbreak iOS 5 on your iDevice, which requires you to be iOS 5 first before proceeding.
Preserve Baseband while jailbreaking iOS 5 on iPhone
iPhone unlockers may already be familiar with PwnageTool and Sn0wbreeze, Mac and Windows only tools respectively, that allow building of custom iOS firmware without the impending baseband update. This time, the iPhone Dev Team have not come up with an update to PwnageTool to support iOS 5. Instead they have integrated the feature into Mac version of Redsn0w.
Sn0wbreeze has always been a port of PwnageTool for the Windows platform. Since there is no PwnageTool for iOS 5, hence no Sn0wbreeze. This is why currently you can build custom iOS 5 firmware for iPhone 4 or iPhone 3GS using only Redsn0w for Mac.
How to jailbreak iOS 5 on iPhone 4 or iPhone 3GS without updating baseband
Coming to the procedure for jailbreaking iPhone 4 or iPhone 3GS on iOS 5 without the baseband update, follow these below steps.
1. Download iOS 5 IPSW, Redsn0w to your desktop. Extract Redsn0w zip file.
2. Now run Redsn0w and click ‘Extras’.
3. Click on ‘Custom IPSW’.
4. Browse and select the IPSW file for your iPhone you earlier downloaded in Step 1.
5. Let Redsn0w build custom IPSW and save it on your desktop.
6. Once the build is completed, you will be notified by Redsn0w.
7. In order to restore your iPhone to this custom built iOS 5 firmware, you need to enter the Pwned DFU mode. Click on ‘Pwned DFU’ on the ‘Extras’ screen of Redsn0w and follow the onscreen instructions to enter this mode.
First make sure your device is both OFF and PLUGGED IN to your Mac.
A. Hold down the POWER button for 3 seconds.
B. Without releasing the Power button, also hold down the Home button for 10 seconds.
C. Without releasing the Home button, release the Power button BUT KEEP HOLDING the Home button for 15 seconds.
8. Now Redsn0w will run the Limera1n exploit and this will make your device accept custom IPSW from iTunes. Let Redsn0w notify you that ‘your device should now be in pwned DFU mode …. In this mode, it should accept custom IPSWs from iTunes’.
9. Now launch iTunes and select your device from the left panel. Click on OPTION key + Restore. Browse and select the custom iOS 5 firmware built by Redsn0w in Step 5.
10. Let iTunes restore your iPhone to this custom built iOS 5 firmware. Once the process is done, you will have a jailbroken iPhone 4 or iPhone 3GS running on iOS 5.
Since this is a tethered jailbreak, you will have to rerun Redsn0w each time and select ‘Just boot’ under the Extras menu in order to boot the device into tethered mode each time you reboot your device.
You can now proceed to unlock iPhone 4, 3GS on iOS 5.
Download iOS 5 IPSW for iPhone 4, iPhone 3GS
Download iTunes 10.5