Is this something which can be done? ideally I want to be jailbroken AND unlocked on the new 4.0 OS. Just thinking can this be done??? BEFORE I decide to upgrade 'officially' to OS 4.0...

In case you have old bootrom, this might work:
Mostly iPhone hacking: OLD BOOTROM + Spirit => 4.0 JB

*Note that if only have one chance of doing it right; if you fail at jailbreaking with Spirit or do those steps incorrectly; you'll have to restore to 4.0 and wait for the next exploit/jb to be made public.

I can confirm that msft.guy's instruction above works perfectly !!!.
Thank you msft.guy and everyone else mentioned on the blog.

ps: msft.guy, can you also mentioned that initial jailbreak with Spirit would need the phone to be activated first. After that, hacktivated custom fw 4.0 can be used later. Everything else is perfect.

S if I understand rigt, you can update to IOS 4.0 even if you have 3.1.3 with old botroom, and JAILBRAKE with SPIRIT?

NO !!!.
The article means:

If you have a 3GS with old bootrom, with 3.1.3 SHSH, then you can restore to stock 3.1.3, activate the phone via SIM+itunes, jailbreak with spirit, then follow msft's instruction to pwn LLB so you can restore custom firmware 4.0 created by pwnagetool 4.01

The reason for that is: if you restore to stock 4.0, even on old bootrom, there is no native Jailbreak for IOS 4 at this time.

Originally Posted by msft.guy

In case you have old bootrom, this might work:
Mostly iPhone hacking: OLD BOOTROM + Spirit => 4.0 JB

*Note that if only have one chance of doing it right; if you fail at jailbreaking with Spirit or do those steps incorrectly; you'll have to restore to 4.0 and wait for the next exploit/jb to be made public.

I think im on the NEW bootrom mate but I do have shsh for 3.13 if that helps?

Originally Posted by dtube

NO !!!.
The article means:

If you have a 3GS with old bootrom, with 3.1.3 SHSH, then you can restore to stock 3.1.3, activate the phone via SIM+itunes, jailbreak with spirit, then follow msft's instruction to pwn LLB so you can restore custom firmware 4.0 created by pwnagetool 4.01

The reason for that is: if you restore to stock 4.0, even on old bootrom, there is no native Jailbreak for IOS 4 at this time.

This procedure fuck my iPhone. Now, I can't reboot that. Can't restore, can't anything.

I can't get out DFU mode. At all, do not try it!

Nice MSFT... nice...

To kick off DFU mode, need restore original 4.0. Only way.

Originally Posted by f41qu3

This procedure fuck my iPhone. Now, I can't reboot that. Can't restore, can't anything.

I can't get out DFU mode. At all, do not try it!

Nice MSFT... nice...

To kick off DFU mode, need restore original 4.0. Only way.

There are many people with old bootloaders who have followed these instructions successfully -- are you certain you had an old bootloader phone? I'd assume (since you're one of the regulars and have been around for a good long while) that you'd know the answer to that question, but I haven't heard of anyone with an old bootloader following the instructions and having the problem you describe. The instructions themselves are safe if you follow them specifically and as mentioned, it is recommended you only attempt if you have a 3.1.3 SHSH on file -- and if that's the case, you should be able to restore to a factory 3.1.3, spirit to JB, then re-attempt the steps above -- they absolutely do work and have been confirmed by many of the members around.

Sorry to hear about your phone