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What are the last 3 digits of your serial number, so I can look up your machine?
If you are able to put the computer in target mode, that would be further evidence that you might not actually have a lock, and at that point reformatting/reinstalling the drive in target mode from another laptop is the most logical step.
From the thread, it appears some people have had success taking it to the Apple Store to get unlocked. Others have accidentally remotely set a password by using the Find My Mac feature in iCloud, in which case it's a 4-digit password. Someone else mentioned that you can change/remove the firmware password by booting from the Mountain Lion DVD and using a tool in the Utilities folder.