Here's the instructions from my 1st post:
Steps to reproduce:
1. Lock your screen
2. Press and hold the search button "magnifying glass"
3. Speak any voice action and the phone will respond. Note: you will not get any visual or audible cues that it is working, but it is!
You see, while the screen is locked, you press the magnifying glass (you don't get any popups or audio cues) but it is working behind the scenes.
The best way to demonstrate this is by saying "Dial XXX-XXXX". Obviously filling in a number of your own. If Google Search (Voice Actions) doesn't have trouble interpreting you, it will automatically start dialing the number and you can take the call.
Edit: If I can some free time from the kids
I'll try to upload a video to youtube demostrating this.