Probably like everyone is saying the hardware. Sell it on ebay or something and then when they come with a new one that works wi the iPhone 4 go out and buy one.
I am sure they will release a new version of the hardware, as mentioned above, this time I hope that they do not make it as snug and allow it to be adjustable so that a iPhone with a case will fit nicely.
I, too, am bummed about the tomtom carkit. I hope tomtom comes out with a new one quickly. I loved that thing! Anyone with a 3G or 3GS want a used tomtom carkit?
sorry to hear that but thats what happens "most", not "all", the time when u get a newer model device, its like my otterbox defender, i sold that bad boy 2 weeks ago to some happy camper on eBay for like $20 shipped, oh well, shizz happens...