In any case, recently I was lucky enough to be able to review two products that make using your iPhone in the car a lot safer. The first product is actually a generic "PDA holder" that as the manufacturer puts it, "holds most handheld PC's." The second is the miCRADLE iPhone holder by Pro.Fit International.
The generic PDA holder takes a pretty good approach to holding your PDA or iPhone. Interestingly enough, it is able to accommodate a wide range of devices by using a spring-loaded latch that is able to expand an inch or so vertically. In fact, the generic PDA holder was even able to hold my iPhone in place with its contour showcase shell on...Definitely a plus in my book.
On the other hand, the miCRADLE is specifically designed for the iPhone and has been custom tailored to fit around the phone without a case. The product designers at Pro.Fit International have done a VERY good job of creating a superior fit and finish. All of the parts are very high quality and nice touches such as felt bumpers on the inside of the cradle have been included.
The only major downside to both of these holders was that installing them was a pain. In a nutshell, the first step was to remove part of the car's console. The next step was to drill holes into the frame behind the console and screw the holder's arm directly into the console. Lastly, the arm needed to be attached to the holder. The upside to screwing these holders into your car is that in the event of a crash or sudden stop, your iPhone would not go flying.
In the end, both of these products provide a good solution to the problem of freeing up your hands while you drive and talk on the phone at the same time. Detailed product shots are available in our gallery.
Generic PDA Holder Pros:
Able to expand vertically to fit a variety of devices
Can accommodate an iPhone with a case
Relatively Cheap
Generic PDA Holder Cons:
Constructed of cheap plastic
Need to drill holes into console for installation
Not so visually attractive
Not able to pivot horizontally
miCRADLE Pros:
Custom Designed for the iPhone
High quality construction
Will not scratch or mark iPhone
miCRADLE Cons:
Need to drill holes into console for installation
Not able to pivot horizontally
Cannot use holder if your iPhone is in a case/holster

I have used one of Pro.Fit International's cradles for an iPhone and it can be used horizontally or vertically. The mount that I got was the UltiMount V2. This mount does not require you to drill behind the dashboard; it attaches to the dash. The head on it pivots easily so you can turn your iPhone as needed.