Originally Posted by dtube

If you have an iphone 2G.
If you have firmware 3.0
If you want to downgrade back to firmware 2.x.
All you have to do is put phone in DFU mode, select firmware 2.x in itunes and restore. You should not get any errors after the restore because the baseband firmware (04.05.04_G) is the same across firmware 2.0 - 3.0.

Err ... I've a 2G iPhone. I have FW3.0. I put the phone in DFU, selected (official) FW 2.0.2, 2.1, 2.2, 2.2.1 and almost immediately it errors out with error 1600, 1601, 1602, 1603 etc.

Right now, the only FW I can get successfully loaded on the phone is the official 3.0 FW. Nothing else works and will error out.

IF still getting 160x error, Try this method
Originally Posted by xtronic from hackint0sh.org
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You can still downgrade 2G iPhone to any firmware even 2.2.1 using my method

You will need ..
1-QuickPwnRC3 download from here ( iphone-hacks.com/downloads/file/138
2-2G Ipsw 2.0.2
3-iTunes 8.2
These steps is to put the iPhone in a mode to allow iTunes to restore to lowers ipsw, if you do DFU the normal way iTunes will give all possibele errors such as 1600, 1601, 20 etc.
Now follow my steps..
A-Open QuickpwnRC3 and follw the steps and select 2.0.2 IPSW and when the screen turn to White color , unplug the USB ( Screen will remians White color).
B-Disconnect QuickpwnRc3
C-Reconnect iPhone
D-iTunes will discover iphone in Recover mode.
E-Shift+Restore to 2.2.1 (with Quickpwn 2.2.5 – http://daniel14.com/QuickPwn-225-2.zip)

Itunes continues the restore process without any erorr

100% works on booth 2G-3G

little tricky a lot of waiting but success
tnx buddy

iphone 2g 3.0.1
quickpwnrc3 with 2.0.2 for entering the dfu
and else ... all folowed
success 100 %
now battery will stay alive for 4 days
LOL