“Now, there are ways to ensure that even after taking an official 3GS update (which you really shouldn’t do!), that you’ll nonetheless be able to revert to a jail-breakable 3GS (this is NOT true for the unlock)…we realize that some of you updated your 3GS to 3.1 anyway. If you want to come back to the world of the jailbreak (but NOT the sim unlock, sorry!) then saurik’s new “on file” server may be able to help.”
So basically what they saying is that Saurik (creator of Cydia) has created an easy way for your i-Phone’s ECID SHSH to be stored on file on a Cydia server. This file is important for future jail-breaking/unlocking.
In short if you still want to jail-break/unlock your iPhone 3GS then don’t update to 3.1 firmware via i-Tunes. The only way to update our firmware for jail-broken i-Phones is to use PwnageTool.
However If you are still curious about updating your i-Phone then trying out the Pwnage Tool, then please read on as there are a few points you may want to consider before going ahead:
1. Upgrading your i-Phone to OS 3.1 will lock your Base-band permanently and there is no downgrading option available at the moment.
2. The Pwnage Tool will only work on (a) the original iPhone, (b) original i-Touch, and (3) i-Phone 3G. The rest cannot be broken at this time.
3. You will need a Mac to run Pwnage Tool 3.1. The Windows version should follow shortly.
You can find links to download Pwnage Tool 3.1 on the Dev-Team website as well as following the guide by Ashish on The Apple Bites. And please make sure to read all the instructions and warnings thoroughly before attempting.
Final note, please be aware that any unofficial unlocking of your i-Device brings with it a void on your Apple warranty. So take care.