Simple recovery/restore mode and DFU are two of the essential modes we need every now and then to archive firmware upgrades and downgrades. Sometimes we have to kick the iPhone out of these modes.
Up to firmware 1.1.4 we had a great helper in iLiberty, for firmware 2.x on 2G and 3G iPhones there are easy manual steps. I have just put them together as a reference.
Get the iPhone into simple restore/recovery mode. When in this mode on the iPhone the iTunes logo and the USB cable is shown (Apple default), or "Steve" (Standard Pwnage) or your custom recovery logo.
1. Disconnect iPhone from your PC/Mac if not done already.
2. Hold Power/Sleep until the red slider shows up, slide to shut the iPhone down. If this aint work hold Power/Sleep and Home until the iPhone shuts down. Put it aside.
3. Start iTunes on your PC/Mac and make sure to have the latest version.
4. On the iPhone press Home button and keep holding it while connecting the iPhone to your PC/Mac.
5. iTunes will detect an iPhone in recovery mode, the iPhone shown the recovery logo.
Get the iPhone into DFU mode. When in this mode the iPhone screen is black.
1. Connect the iPhone and your Mac/PC
2. Shut down iTunes
3. Hold Power/Sleep until the red slider shows up, slide to shut the iPhone down. If this aint work hold Power/Sleep and Home until the iPhone shuts down.
3. Hold Start/Sleep and Home for 10 seconds (I count like 100, 200, 300, ..)
4. Let go of Start/Sleep but keep holding Home until...
5. ... iTunes starts up and finds an iPhone in restore/recovery mode. The iPhone screen is black.
Kick the iPhone out of simple restore/recovery mode and make it reboot.
1. Connect iPhone and your PC/Mac, quit iTunes.
2. Hold Start/Sleep and Home for 10 seconds (I always count 100, 200, 300,...)
3. Let go of Home button but keep holding Start/Sleep until the Apple logo on the iPhone screen shows up.
4. Let go of Start/Sleep, the iPhone will boot
Kick the iPhone out of DFU mode and make it reboot. I always disconnect iPhone and Mac/PC but can be done even when connected.
1. Hold Start/Sleep and Home until the Apple logo shows up on the iPhone screen. This may take up to 30-60 seconds.
2. Let go of both buttons, the iPhone will reboot.
hope this helps