No matter how accurately I held the sleep and home buttons to put my 1.1.2 phone into DFU (white screen) mode I could never get it to turn white and I kept getting error messages after I did so. I held the sleep and home buttons for 10 seconds, released the sleep button and kept holding the home button until iTunes recognized my phone again, at which point an error message pops up and says my phone couldn't be recovered or something (error -11?). On a whim after that I simply disconnected and reconnected my phone and voila, the white screen appeared. After this I was able to downgrade by holding shift and pressing restore to find the old firmware that I downloaded onto my computer. Hopefully this will work for all of you 1.1.2 users who are probably as frustrated as I was.