I should never have doubted you – I take it all back! 🙂

thanks Jaap, but actually those are the correct instructions. DFU should not be used for flashing to the PwnageTool'ed version of iOS 4.

The timing difference for Recovery as opposed to DFU is only very slight (a few seconds), but the method is the same (hold home + sleep). The big difference is highlighted in the final line of each set of instructions.

I'm afraid that's not nearly enough detail for me to provide an answer. I believe the guide should be more than enough to guide you step-by-step, and if not, the links i've provided within the guide should walk you through any steps that might need extra clarification.

However, if you need to simply back up and get back to a usable iPhone, simply click the restore button in iTunes and you'll be back on iOS 4 stock. If you're running the Wi-Fi Sync utility, make sure it's turned off or uninstalled before restoring.

i have tried to follow you steps and managed to make firmware through (PwnageTool 4.0) but when i put my iphone into recovery mode and tried to restored, it shows an error and now i am able to use my iphone if i don't update and restore my phone, please tell me what i have to do.

thank's

Short answer: sorry, you're out of luck for now.

The problem is that your device must be jailbroken before you can to upgrade to a jailbroken custom firmware of iOS 4. There's nothing out right now that can just jailbreak your current firmware installation, so you need to be able to install a jailbroken custom firmware (made by PwnageTool).

You can't do what I did (downgrade to 3.1.2 and then jailbreak that) because you weren't previously jailbroken (which would have provided you with the ability to downgrade to a firmware and then use this guide).

We may see a new jailbreak from Geohotz soon enough, but I wouldn't hold my breath — he has stated on Twitter that he doesn't even have an iPhone 4 to develop with.

Thanks Scott – and thanks to all the other people who have left some kind words. I wont' respond to all of you, though, since I don't want to clutter up the guide's comments with \”thank you thank you\”. Many of you are posting little extra tips and I'd like for people to get to them easily without wading through all of my gratitude.

Worked like a charm the first time.

I confirm that the following (final) step WORKED (i.e. – NO "error 16xx"):

– from iTunes, put the iPhone into "Restore Mode" (NOT "DFU mode") and option-restore PwnageTool 4.01's custom-built IPSW file)

iHackintosh article: "What is Difference Between Recovery Mode and DFU Mode" is here:
http://www.ihackintosh.com/2009/06/recovery-mode-…

Maybe your blobs were already backed up (simply load up cydia to do this), or you were on the right firmware with the right circumstances to begin with (non-Spirit jailbroken 3.1.2 or 3.1.3).

Actually, I don't think this is true. I certainly didnt backup any blobs, and I just followed your guide just fine without them, though I did add the server redirection into my hosts file. I think as long as your iBoot is good, then all is happy with the world…

If Restore's progress bar hangs on the iPhone screen:
The progress bar on the iPhone screen during the restore process hanged for a too long time, so I decided to try a 'magic trick': I downloaded and run blackra1n and hit the "Make It Run" button and the progress bar on the iPhone's screen began to move again.

If you get error '1600' during restore:
Likely you switched into DCU-mode instead of Recovery Mode. (iTunes talks about Recovery Mode in any case, don't believe it.)
To leave DCU-mode, unplug the USB cable from iPhone and keep the Home button held down during plugging the cable in to enter the Recovery Mode.

I hope these suggestions are for help!

@Scott M. Shell
thanks for the kind words. As for clarification, I'll do my best:

1) my knowledge of the Terminal is that of a toddler's at best. I read guides liked the ones I linked to, and I follow them once I've confirmed from others that they work. I didn't have to flush my DNS cache with any extra commands. The IP address is still in my /etc/hosts file, and I haven't even commented it out.

2) I'm thinking this may either have to do with the way you restored your phone. I simply put my iPhone into restore mode, and not DFU mode, before upgrading to jailbroken iOS 4. I think that's the error you're encountering, based on my own experience and this quick bit on SimonBlog from 2008:

http://www.simonblog.com/2008/10/07/iphone-jailbreakupgrade-more-on-itunes-1600-error/

I know it's not the same firmware, but it could be worth a shot.

my interpretation of RedSn0w info:

Serial Numbers
<40 = safe
40-45 = iffy (you should probably check the iBoot, instructions are in the guide)
>45 = newer bootrom, you're out of luck for now

What if it is above 40?

Please clarify:

1) at what point does the /etc/hosts file need to be reverted (by commenting it out, as follows, with a pound sign at the beginning: #74.208.105.171 gs.apple.com), followed by a flushing of the DNS cache, via the following command (in a Terminal.app session)?:

dscacheutil -flushcache

2) My iPhone OS 3.1.2 reversion (from ios 4.0, non-GM, 23JUN10 version) and subsequent jailbreak worked; however, the final step (ios 4 jailbreak via iTunes' DFU mode restoration of PwnageTool 4.01's customi-built IPSW file) FAILED with an Error 1600.

Ideas?

Very kind regards,

-=s/m/s

Any time — and that should be Pwnage 4.01, btw. Oops.

Thanks Thomas

Yep, you can use this guide. Serial numbers under 40, according to the Dev Team notes in redsn0w, are the good ones.