From the Motorola Website:
How can I voice dial on my phone?
There are two methods to voice dial from your phone:
1. Use Google Search
2. Use Voice Dialer
To use Google Search to voice dial:
1) Press and hold the SEARCH button.
You’re prompted to speak.
2) Say “Call” followed by the name of the contact you want to call.
If Google search by voice finds a match, it dials the contact’s default number.
To use the Voice Dialer Application
1) Open the Applications Menu
2) Touch Voice Dialer
3) Say your command
1) Call "John Doe"
2) Dial "John Doe, home"
Bluetooth Voice Dial Issue
1) Droid/Milestone supports one-touch voice dialing and full Bluetooth voice conversations.
2) It does not support hands-free dialing via Bluetooth, and Motorola is aware that it does not.
3) On Droid, you can answer a call or initiate the 'last dialed call' by pressing and holding
the call button on your headset.
4) You can initiate voice-dial using the Google Search or Voice Dial options from the phone itself.
5) Voice Dialing cannot be initiated from a headset, you must turn it on from the phone.
6) At this time the using Bluetooth for voice dialing only supports dialing last number.
Will there be an update?
Motorola is currently evaluating possible solutions for providing voicedialing over Bluetooth.
Motorola does not have a timefame defined for this; however the update will be provided through a software update process. A full featured version may be available via the Android Marketplace