Accidentally posted this in the iPod forum, hopefully this is the right place. If not let me know where I need to post this for it to be "on topic".

I am downgrading my friends iPhone 3G to 3.1.3 because it's much too slow with 4.2.1.


I am using the following method:
http://www.youtube.com/watch?v=KGqul3wjKJc


I had a few questions, if you all wouldn't mind:
It is currently jailbroken using redsn0w, will this cause any problems?
Will this remove any and all installed apps/settings/etc from the phone, or will they be carried over? If it does, is there a method of downgrading that saves all of the/some of the above?

Thanks for any help you can give.

1) No, it being jailbroken won't cause any problems. Restoring will remove the jailbreak (unless you restore to a custom firmware).
2) Yes, it will remove all apps/settings/etc. from the phone. It's *possible* that you will be able to restore from a current backup to the 3.1.3, but I think it's somewhat unlikely. They change the file format for backups as well as the file format for the databases and settings that are being backed up. Application settings will transition so long as it allows you to set 3.1.3 up as a restore from a backup. If it forces you to set up as new, app data will only be able to be migrated manually (e.g., use iFunBox / DiskAid / iPhoneBrowser to actually copy the application data from the phone on 4.2.1 and then copy it back to the same directories on 3.1.3)