I own a SIM locked Tab from Bell Canada and I'm working on unlock the SIM lock. I just used Z4root get the root privilege and was about to use RootExplorer to backup the /EFS folder to a microSD card. But the RootExplorer didn't show any file under the /EFS folder.
I think you should put in another carrier's sim card and verify lock/unlock.
Cromed makes a good point. Is Superuser installed? And have you installed the latest busybox from the market?