If you want to upgrade to iOS 5 but you have locked iPhone unit (aside from 4S), you might want to consider the ability to preserve your baseband to be able to unlock. UltraSn0w (V 1.2.4) unlock was just recently released for iPhone 4/3GS/3G that runs iOS 5. Here is the list of basebands that are compatible for unlocking:

iPhone 3GS: 4.26.08, 05.11.07, 05.12.01, 05.13.04, 06.15.00

iPhone 4: 01.59.00

You can follow the procedure in updating iOS 5 without updating your baseband for Windows and Mac in our previous posts.

In order to unlock your iDevice, you need to jailbreak first since it needs Cydia to download the UltraSn0w 1.2.4 package. Make sure that your baseband is listed above or else the unlocking process will not do.

A release note from the Dev Team is posted for users of iPhone 3GS and other possible baseband downgrades for some situations:

Note: there’s a special “trick” that iPhone3GS owners with baseband 06.15 need for iOS5. During the new setup screens you see when you start iOS5 for the first time, you’ll be asked about Location Services. Be sure to select “Disable Location Services” when asked! Later on in the setup, you’ll have the chance to turn on Location Services again when asked if you want to use “Find my iPhone”. It’s fine to turn it back on at that point, if that’s your desire (or you can always go in and enable it in Settings.app).

Also, some iPhone3GS users with the 06.15 baseband may have tried to install iOS5 using a stock IPSW (even though you should never ever try to use a stock IPSW if you’re an ultrasn0w unlocker). If you did try this, your baseband is probably in an inconsistent state, and you’ll need to reflash the 06.15 baseband again (using redsn0w). Be very careful if you use redsn0w to reflash the iPad baseband — don’t interrupt the process! And please avoid using stock IPSWs in the future  Unlockers should never go near stock IPSWs.

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.

Having an unlocked iPhone is what almost every iPhone users wanted to have. This is because you can switch to any carrier any time you want. Sn0wbreeze is the best tool to use if you are running on a Windows OS machine. With Sn0wbreeze, you can preserve the baseband of your iPhone while upgrading to iOS 5 if you are from iOS 4.x.x.

The following steps will upgrade your iPhone to iOS 5 and at the same time will preserve your baseband for unlocking purposes: (Note: can be used with iPhone 4/3GS/3G)

1. Download Sn0wbreeze 2.8 Beta 8.
2. Launch Sn0wbreeze and click OK and the blue arrow below.
3. Drag to the gray box on Sn0wbreeze the iOS 5 firmware but make sure that the firmware for your device is correct.
4. After verifying that the firmware is correct, click the blue arrow below and click on “Baseband Preservation Mode”. Click NEXT.
5. Sn0wbreeze will then start to build your custom firmware. After finished, the custom firmware will be saved to your desktop. Verify and click OK.
6. 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.
7. On the DFU Pwner screen in Sn0wbreeze, click START.
8. “iREB” will start and will place your iPhone in Pwned DFU Mode. Close out Sn0wbreeze completely after clicking the confirmation screen.
9. Launch iTunes so it will recognize that your iPhone is in Recovery mode. Click OK.
10. Hold ‘Shift+Restore’ and browse to the newly created firmware in your desktop.
11. Wait for the Restore process to finish and you should have the same unlockable baseband.

Enjoy having an iOS 5 while preserving your baseband!