So my friends iPhone screen went black. It still gets calls coming into it, but the screen wont turn on. I think it just needs to be restored.

The phone was unlocked and jailbroken. I dont have my iPhone anymore so I havent been paying attention to the current firmware and what not.

How should we go about restoring it, jailbreaking it, and unlocking it? I dont want to upgrade to a fimware thats not unlockable. Any info would be great.