Voice Dialing Issues
I am sad to say that the voice recognition failure is permanent on most of the E815 phones. Your phone will likely never support voice dialing again, even though the cause remains unknown.
I too had the peculiar problem of pressing the voice button and hearing a beep, but no voice prompt ("Say a command"). When I researched the issue, I found a plethera of similar problem reports. Very few reported recovery after simply restarting the phone. I even found one report of Motorola tech support giving up and instructing the owner of the phone to have it replaced.