Thought I would share some of my findings.
I work for a major mobile network provider and have played with the RIM blackberry devices.
The RIM 8100, 8800, 8820 (on the GPRS/EDGE networks) support voice dialing.
Here is what I did.
Created a cable with a 2.5mm stereo male on each side. In the middle I have attached a mute/momentary switch. By holding down the switch for 2 seconds, prompts for voice dialing. I can say, "call John Doe Home" or "call 201-555-1212", or "call John Doe Work".
I attach the cable to my BB and also to my cell phone port on the comm system. The mute/momentary switch hangs loosely outside the audments box. The switch acts as a mute, prompt for voice dialing, and a disconnect.
I have tested this at 60+ mph and it works great.
I also have this working with my Garmin 2820, buts thats another story.