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.

iPhone Jailbreak Pros have released v2.4 of Snowbreeze / Sn0wbreeze app that now supports Ultrasnow unlock for iPhone 4 devices. The support is limited to old basebands only. So, if you have performed the jailbreak process using our iPhone 4 jailbreak guide, you can use ultrasn0w to unlock iPhone.

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