The kit has its own GPS chip which is supposed to be more sensitive than the GPS chip built into the iPhone. The car kit is listed as 'coming soon' at the U.S. Apple Store. It's expected to cost US$119.95, and when added to the cost of the TomTom app brings the total to more than $200.
That high price has caused some to question paying that much money for a GPS unit, when a standalone model can be bought for less. We'll be following the user comments on the car kit, and hope to get one ourselves for testing soon.
The whole category of GPS solutions for the Phone is moving very fast, and it seems almost every week a new app comes out with more and more features giving the iPhone parity with the separate units you can buy.
TomTom hopes to offer a high performance solution while still letting a person carry one device that does it all, unless you count the car kit as another device, of course.
Thanks to Stu for the tip.