If you are a Mac user and wanted to upgrade your iPhone (4 or 3GS) to iOS 5 while you can preserve the unlock, this is the best procedure to follow. This is for the preparation of unlocking your iPhone again using UltraSn0w in the future.

RedSn0w 0.9.9b5 is the tool you need in upgrading to iOS 5 using your Mac computer. This is because the developers in the Dev Team have added the baseband preservation tool to RedSn0w which was previously available in the Pwnage Tool. Please take note that this is not a jailbreaking procedure. Instead, this will only preserve the baseband of your iPhone so you can unlock using UltraSn0w in the future.

Steps in preserving the baseband for iOS 5:

1. Download RedSn0w 0.9.9b5.
2. Launch RedSn0w and select ‘Extras’ and ‘Custom IPSW’.
3. In your Mac, select the iOS 5 Firmware (~/Library/iTunes/iPhone Software Updates/)
4. Select ‘Pwned DFU’ from RedSn0w after building the new firmware.
5. Start your iPhone to DFU mode: Hold ‘Home+Power’ buttons simultaneously for 10 seconds, release Power button while continue holding the Home button for another 10 seconds. RedSn0w will then put your iPhone in Pwned DFU mode.
6. Close RedSn0w completely and launch iTunes. It will recognize an iPhone in Recovery mode.
7. Hold down ‘Option’ key on your Mac keyboard and click ‘Restore’ while selecting for NO_BB firmware which you had recently created. NOTE: Make sure to select the NO_BB firmware or else you will update your baseband.
8. After restoring, you will now have iOS 5 in your iPhone while preserving the baseband. You can either jailbreak your iPhone now or wait for UltraSn0w update for iOS 5.