Despite all the warnings if you upgraded your iPhone to the latest iPhone OS 3.0 Beta without a developer account you must be locked-out from normal phone functionality, downgrading your iPhone to an earlier version is pretty straight-forward but downgrading your baseband (which is responsible for the unlock being not functional anymore) is not possible with newer versions, You can downgrade iPhone OS 3.0 To earlier 2.2.1 version using the following guide.
- Power-off your iPhone and enter DFU mode using instructions below.
- Push and hold Home and Power buttons on your iPhone simultaneously for 10 seconds.
- Release the Power button but keep holding Home until the computers beeps recognizing the USB device.
- You should be in DFU mode now.