Preserve Baseband 01.59.00 during iOS 4.2.1 firmware update (on iPhone 4) – Preserving specific version of iOS baseband allows you to unlock it when the official unlock tool is not released yet. For iPhone 4 users, luckily, newer version of TinyUmbrella allows you to update iPhone 4 to iOS 4.2.1 while preserving baseband 01.59.00.
For your information: Currently, iPhone 4 iOS 4.2.1 is jailbreakable, you can untethered jailbreak iOS 4.2.1 on iPhone 4 easily using Greenpois0n RC5. But basically, iPhone 4 iOS 4.2.1 is on baseband 03.10.01. When you update your iPhone 4 to iOS 4.2.1, it will also update your baseband to 03.10.01. And meanwhile, there is no unlock tool for iPhone 4 iOS 4.2.1 baseband 03.10.01.
So, if you planned to jailbreak your iPhone then unlock it, then you have to preserve your iPhone 4 baseband 01.59.00. And here it is how to preserve baseband 01.59.00 using TinyUmbrella 4.21.05 or TinyUmbrella 4.21.06.
9 Steps to Update iPhone 4 to iOS 4.2.1 and Preserve Baseband 01.59.00
3- Now run TinyUmbrella tool
4- Click on [Save SHSH] button and make sure iPhone 4 iOS 4.2.1 SHSH blob is listed there
5- Then click on [Start TSS Server] button. Note: it will kill iTunes.
6- Now open iTunes.
7- Hold down the SHIFT (Windows) or Alt/Option (Mac) key and hit the Restore button on iTunes.
8- Then browse and select your downloaded iOS 4.2.1
9- An error 1013 message will be displayed. Simply ignore this as it is normal. Then click on [OK] button
Walla.. now you’ll have iOS 4.2.1 firmware runs on your iPhone but the baseband is still 01.59.00. So now you can proceed to jailbreak the iOS 4.2.1 then unlock it. Follow this step-by-step guide on how to jailbreak iOS 4.2.1 (untethered) using Greenpois0n.