iPhone 3GS Firmware 3.0 how to restore and NOT update?

[JReynolds]

I'm selling my iPhone on 3.0

The guy wants it to to stay on 3.0 but I need to erase all the data in order to sell it.

I have less than an hour to figure this out PLEASE HELP

 

[bytethese]

I'm selling my iPhone on 3.0

The guy wants it to to stay on 3.0 but I need to erase all the data in order to sell it.

I have less than an hour to figure this out PLEASE HELP

Welp, I wonder what you did since it's been more than an hour.

Personally I would have told the guy he gets an updated phone as I would have Erased All Content and Settings so that none of my personal data could be recovered. If he wanted to be able to unlock, then I would have performed the necessary steps to backup my SHSH with Cydia then using Saurik's iTunes "hack", I would have restored a custom 3.0 (personally I would do 3.0.1 so there's no SMS vulnerability) and then you'd be fine.

 

[dhlizard]

Most of us would have made the phone ready to sell before actually selling it, not the other way around.

 

[Applejuiced]

You can JB it on 3.0 with Redsnow or blackrain.
And then assuming you have untethered JB restore it to custom 3.1.3 with an IPSW created with pwnagetool.
Thus preserving an unlockable bootloader and JB along with a restored firmware that has none of your info on it.
Its a little involved.
If not just manually delete all your stuff from it like contacts, texts, email accounts, apps, log out of your itunes account etc...