I have experienced and read that the BT voice dialing in the Hero is pitiful. It is not true voice dialing. I have to tap the voice dialing widget, wait for the tone, speak very carefully, then have to go back to the Hero to tap the OK or select the specific contact number I want to dial. (Home, office, cell, etc.)
This is especially frustrating when HTC had it perfect with the Touch Pro. I had zero problems voice dialing with that phone and it was truly a leave the phone in your pocket/case/whatever dialing. Hold the BT button down, wait for the tone, speak the contact with or without specific type of number, wait for the voice to confirm ("call John Smith mobile?") and say "yes". That was it. The phone would dial. Why couldn't HTC have it that way on the Hero? It shouldn't be a WinMo vs. Android thing.