This seems to be a known issue. Sucks for me since adding my work exchange account forces my to have a lock screen w/ a PIN. This was real fun the first day I noticed it - nothing like driving and troubleshooting my phone. I found an app called "No Lock" that is a widget that can toggle the lock screen on and off. When I get in my car I disable the lock screen (which isn't so bad since I usually have to turn BT back on anyway).
I learned that it's designed this way. If not, someone could use the headset to access the phone, since voice command can do more than just dial. It's considered a security risk. I find this reasonable if not super-compelling.
Hmmm doesn't sound like a convincing reason to me.
Bluetooth devices need to be paired before they should be able to access your device. What prevents a person from accessing your phone via BT when its unlocked then?
On my Droidx I can control the music player via my BT headset when the phone is locked... I just cannot issue voice commands.
I recently bought a Jawbone ICON and installed A2DP. I installed their free 411 app but I need to delete it as it's just a glorified autodialer. Once I do that I can try the voice dial while locked again. I wonder if A2DP support will change that behavior.