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.

The famous iPhone Dev Team have released another iPhone Jailbreaking utility - "QuickPwn", as the name suggest the Windows only batch files let users jailbreak iPhone more quickly and easily without requiring a full restore, the software is labeled as pre-release developmental snapshot so better handle with care.