I am in the middle of this too. Without a voice-dial feature, then the next best thing is a useable vehicle-mounted touch screen so you can list your contacts and then touch their name to dial.
This is obviously safer than holding a phone in one hand, dialing with the other and steering with your knees. Or doing the same on your phones' contact list.
I bought a Garmin 660 GPS. One of its features is that you can enter names and phone numbers. The unit fits on my dash via the Garmin beanbag and is pretty solid. I can keep my eyes up and ahead and just use one hand to scroll for the number and push on it to dial the iPhone.
This GPS and the iPhone hook up very well with bluetooth
When a call comes in, I just touch the screen, it answers and I can talk hands-free.
The Garmin, like all such devices, connects to the car's stereo system by the sucky fm transmitter system. This is a subject all to itself, as you will find if you pursue this.
The Garmin has a voice dialing feature! But, the phone has to have one too, or it obviously won't work.
So, right now without a voice dialing feature on the iPhone you will be stuck with something like I described to be at least semi-legal and reasonably safe.
It sounds like your work, driving around making calls, might benefit from having a GPS anyway.
This is why Apple needs to have both a voice dialing capability and soon. And GPS is actually getting to be a requirement, not just a toy.
Let me know if this helps or you need more info. I think a lot of people are faced with this problem.
