I covered a fun bit of technology from Griffin Technology over the last couple years called the AirCurve. There is a model for the iPhone 3 and one for the iPhone 4. The technology is simple in that it channels the iPhone’s speaker audio output though piping that enhances the db level so you get much more volume. In the case of the iPhone 4, about 10db, which is enough to make the iPhone usable in the office as a speakerphone.
Now, Griffin Technology has introduced a version for the car. Similar to the desktop version, except with a window mount and a boost of 25db! That is enough to hear the iPhone speaker output while driving, without the need of additional wires for power or external speakers. It has an opening in case you still need to run a wire to charge your iPhone on the go, but it isn’t needed to get the louder speaker output that normally would require wires at least to a speaker. This should be a hit in the areas of the US that require handsfree phone usage.