Upgrade 3.0 to 3.1.2 with customized firmware
 

Ok, first I Apologize for the English, I cannot write but but I can read dutch language very well.
Then I appreciate all the people who put effort into helping everybody to the latest SW versions on the Iphone!
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I have been reading the forum but I am a noob for this and require some assistance.[/FONT]
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[FONT=Verdana]Let me explain: I have an Iphone 3GS 32GB with SW version 3.0, jail broken and unlocked in Hong Kong. So far everything works fine and when changing cards for carriers while I am in Europe and china works flawlessly. When I upgrade to 3.1.2 with a customized SW version. I want the same again (jail broken and unlocked) on my iphone.[/FONT]
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[FONT=Verdana]I have seen various customized version of SW 3.1.2 on the internet but I am not sure what to do. They are activated or not activated, and there are more differences I hope someone is willing to explain to me....[/FONT]
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[FONT=Verdana]My computer is on windows 7 and I have no access to a MAC

Questions:

1) Can anyone advise me on a trusted customized 3.1.2. software version that I need to have when I want to go from 3.0 to 3.1.2 through Itunes and still have a device that is jail broken and unlocked for use in china and Europe?
2) After installing this customized firmware 3.1.2 version from this tread with ITunes 9.01, will my baseband be upgraded or not?
3) When I perform this upgrade to 3.1.2 and the baseband is not upgraded, will I be able to unlock & jailbreak again in the future when the new baseband is cracked? (With respect to the warnings of the devteam and announcements from Apple to fix the unlocking)
4) What is the difference between activated and not activated 3.1.2 SW version and which version do I need considering my current situation as described here above? [/FONT]
[FONT=Verdana]5) I read about small and big root partitions. What is the difference between a small and big root partition? More pre-installed programs?
6) What should I definitely NOT do while upgrading to turn my Iphone 3GS into a useless phone or expensive IPod?
7) Would it be better to stay on 3.0 instead of upgrading now?

Thanks for all your help!![/FONT]
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Update with a 3.1.2 custom firmware with activation, then unlock with ultrasn0w. (available on Cydia).