Welcome to the forums!
A couple of points:
1. Unlocking the device allows you to use another GSM carrier besides T-Mobile. It has no bearing on your abilty to use data without a BlackBerry Data plan.
2. You will have to call T-Mobile to have the data enabler added to your account.
3. Required data plans for T-Mobile Blackberrys are probably inevitable. Don't know when this will go into effect, though.
1st Step in Troubleshooting: Do you have a BlackBerry Data Plan?
2nd Step in Troubleshooting: Pull the Battery.