I received an iPhone 3G from a friend that has been de-activated, restored to manufacture settings, running firmware 4.2.1, and non-jailbroken. What I'm finding is that I cannot turn the phone on/off with the sleep/wake button. I can press it down but I never get the off slider button on the screen. This is making it extremely hard for me to get the phone into DFU mode. I've got an AT&T sim card on the way to get me past activation since I'm going with a different carrier.
Does anyone have any suggestions on how I can get past the non-functional power button?