How to unlock iPhone 4 with iOS4.2.1

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You know that within the next days an unlock for 3G/3GS will come out. But for iPhone 4 it will take longer.

So if you are still on baseband 1.59.00 (with firmware 4.0.1 or 4.0.2 or 4.1), you can unlock. The problem is how to upgrade to 4.2.1 without upgrading the baseband.

Chronic (of the group that released greenpois0n jailbreak) just used TinyUmbrella method with the kick option. I tried this yesterday, but it didn't work for me. So better don't try. There's a check in firmware to have a current baseband or something.

Here's another way that I consider from a trustworthy source:
Preventing Baseband Update - The iPhone Wiki

Please note that you need a Mac and command line tools, you need to find the keys etc. so this method is not for beginners. I'll try this today and will give you feedback. If you also want to try, leave feedback here also.