iPhone firmware 1.1.2 hits iTunes

It's already been available -- and hacked -- for a a few days now, but iPhone firmware 1.1.2 has finally reached iTunes, the natural home of all things iPhone. We honestly haven't noticed much more new since we started poking around -- the .m4r ringtone hack seems to be back, and custom ringtones are now broken out in their own list -- but we know you can't resist the siren call of the latest version number. Go on, you'll be fine -- and it's not like getting back to 1.1.1 is any great feat.

http://www.engadget.com/2007/11/12/i...2-hits-itunes/

jailbreak is for 1.1.1.
i am uk on 1.1.2
how do i downgrade to 1.1.1. - the post says it is not hard. how come?