Why buy one of those fancy 'schmancy' solutions, when you can get yourself handsfree for next to nothing?
First, you will use your earbud for speaker.
Second, get some velcro tape. Stick the female side on your dashboard, or anywhere where the phone is vertical, so you can easily see the screen. Attach the 'male' side of velcro tape to your Blackberry device.
Slap the blackberry on the velcro.. remove it, make sure it's not too strong and allowing the tape to be removed from the car itself.
After a few applications of blackberry on velcro, you'll find it removes easily but stays on regardless of the driving conditions (bumpy, etc).
I leave my Blackberry on my dash at all times, when expecting calls, the earbud is also in the Blackberry. I can easily glance over when a phone call comes in, identify the user, answer the call, all without taking both hands off the wheel, and focusing on driving.
The blackberry's microphone is more than adequate for talking while driving...
Similarly, if you want to spend a little more money, you can buy a headset if you want.. buy why go crazy when you can do it on the cheap and without rediculous protruding plastic crap on your dash?