As a followup to their "yes we CAN unlock the 3GS with ultrasn0w!" post — itself a response to the release of the competing purplera1n cracking tool — the Dev-Team posted this temporary (and technobabble-heavy) solution:
Remember we warned you to stay away from any updates to 3.1 if you want to be able to jailbreak or unlock your 3GS.
Well this is an additional message to all you 3GS owners that would
like to jailbreak your device sometime soon, but this advice comes with
a warning! A warning that if you accidentally upgrade to 3.1, you will not be able to use Ultransn0w, so please re-read and double check this warning at the bottom of this post before proceeding.
You may have read or heard about techniques to capture files during
the iTunes restore process. These will be required to jailbreak your
phone in the near future, most of the methods involve icky USB snoops.
Well, there is an even better and more reliable method to get your hands on those lovely files.
During the restore process iTunes nicely keeps these oh-so-top-secret-files in a lovely accessible place for us to copy out and backup, that place? /tmp on Mac OS X or %TEMP% on Windows. Thanks Apple ‚Äî handy!
The downside to this approach is that you actually need to go
through the restore process to get these signed files, which has risks
if you are anywhere near 3.1 or 3.1 beta 🙂
If you are ready to proceed and you know the risks we‚Äôll get down to the nitty-gritty –
So during a usual recovery with iTunes, your signed iBEC is written
to /tmp and during a DFU mode restore the signed iBSS is written there
also. To be sure, restore in both modes one after another to be able to
grab them both. You‚Äôll need to keep an eye on the temp directory and
copy it before it is deleted again by iTunes. I‚Äôm sure some nice folks
will create a tutorial about this, we‚Äôll link to the first person who
makes a good one.
Should you choose to accept this mission, act fast, this needs to be
done quickly! But again, always, always double check here to see if 3.1
has been released, if is has, then don‚Äôt do this.
WARNING!! – DANGER, WILL ROBINSON! – NB! – REMEMBER!
IF YOU CARE ABOUT ULTRASN0W, BE VERY CAREFUL WITH THIS METHOD!
Do not attempt this if you have downloaded the 3.1 beta. You do NOT
WANT TO accidentally restore your device to 3.1 beta ‚Äî you‚Äôll lose
ultrasn0w if you do! BE WARNED 🙂
Also, see our iphone 3g and 3gs unlock tutorial: How to Unlock iPhone 3G and 3GS Using ultrasn0w