I'm trying to unlock a 3G 16GB model for a friend.
His current firmware is 3.1.2 (JB/unlocked) 5.11.07

SO I follow the Redsn0w JB guide and download the firmware from that modmyi link: iPhone1,2_4.0_8A293

I go to iTunes and do Option>restore to this file. It does the extraction and then checks with Apple and I get a message saying that it can't be installed as the file is the wrong build.

So I didn't even get to the stage where I would launch Redsn0w.

As far as I know the 3G build is the 1,2 and the 3GS is the 2,1

Any suggestions?