I just want to make clear that I am talking about Google Voice Search. It is similar to TellMe and Yahoo OneSearch Voice.
It is NOT voice turn by turn direction.
I think voice search feature is added newly in google maps 2.2.1 version. So if you uninstall and install the Google Maps again , you may find this feature.
After installing the new google maps, just open the Google maps and hold the "Left Convenience Key" to speak the business name like pizza etc. You have to be in Google Maps to use Voice Search feature.
"Left Convenience Key" button is located on left side of blackberry which is usually used for shortcuts. Check below link to locate the Left Convenience Key button Make Your Convenience Key More Convenient : BlackBerry Edge
As I said earlier, I am able to say voice commands by pressing "Left Convenience Key" button. But the search didn't work for me.
Let me know if you guys have any doubts.