This is what tomtom wrote back to me when I asked about the car kit not working, but thanks to those here who figured out an easy fix:
Thank you for contacting TomTom Customer Support. We apologize for the delay in responding to your query. My name is Abby. We are always happy to help.
The TomTom car kit is currently available only for the regular iPhone, iPhone 3G and iPhone 3G S. The iPhone 4G being a newly launched product from Apple, it has not been tested yet with the TomTom car kit. Hence we regret that we will not be able to comment on its compatibility with iPhone 4G as there are some significant size differences between the two models.
We are receiving lot of requests from customers regarding the same query and we have already forwarded them to our Product Development team for further review. We take all customer feedback received very seriously in the future development of our products. Suggestions are gathered and organized to understand the areas our customers are most interested in enhancing.
Our Product Managers review all feedback to determine future enhancements and products. Many of our current products and updates offer features based on customer suggestions.
In order to be kept informed of current developments, we suggest you to subscribe to our Newsletter. For more information, please click on the link provided below. If you are unable to click on the link, please copy and paste it into your internet browser.
http://www.tomtom.com/2091
I hope I have addressed your question appropriately. Please let me know if I can be of any further assistance in this matter.
We value you as a customer and your complete satisfaction is our prime concern.