As far as i know there are three types of boot modes for the iPhone.
1) Normal boot into operating system
2) DFU mode showing iTunes logo
3) DFU mode with blank black / white screen
Anyone care to elaborate on these different types of boot up mode? The only thing i know about 2 & 3 is that if you try to restore from 1.1.1 to 1.0.2 in mode 2 then you'll receive Error 1. But if you change to mode 3 then this error doesn't appear. Strange...