This info applies to all iPhones especially FW 1.1.3

Ok many of you might run into this issue with downgrading from 1.1.3 or 1.1.2 of iTunes giving you an error code 1 when trying to downgrade firmware.

To start off I am running a power pc mac with leopard & iTunes 7.6.

After much searching & reading post after post of others in same situation. Folks saying you need to downgrade iTunes to 7.5 etc etc etc.

When downgrading firmware you must put the iPhone properly into DFU mode.

This is how to achieve DFU mode. You can do it on every phone:
Attach the phone to the pc
Turn the phone off
Hold power and home together for *exactly* 10 seconds
Release power but keep holding home until the pc beeps as a USB device is recognized.
At no point will the display come on. Now your restore should work.

Now after you have downgraded your firmware iTunes will give you error code 1015 this is normal.

But you will find your iPhone in recovery still. To reboot the iPhone use of iNdependence should boot you ! But after downgrading no matter what you try iPhuc etc etc etc can boot the iPhone.

You need to do another iphone restore using the option key and select the version.

After you have done the second restore and get your error 1015 you can close iTunes open iNdependence and your phone will boot.

This is something that is coming up allot recently with 1.1.3 downgrade & restore. It is not an issue with iTunes version as I found the above info works on XP & Vista. Its an issue of not putting the phone in the proper mode to downgrade firmware.