We first heard about TomTom's car adapter that boosts the functionality of their upcoming GPS iPhone app at WWDC, but some new information has 9 to 5 Mac thinking that the device will work the iPod Touch as well.
iPhone owners will be able to purchase and use the TomTom software and maps without the Car Kit hardware accessory; however, the Car Kit for iPhone was designed to enhance the software by addressing several of the limitations mentioned above. For starters, the Car Kit includes a separate GPS receiver that performs better than the one built into the iPhone; Murray said this receiver is closer to what you'd find in a dedicated GPS unit. The TomTom app uses this receiver when your iPhone is docked in the Car Kit, allowing for improved real-time navigation, especially in cities with large buildings or in locations with lots of trees or other natural obstacles. The Car Kit also includes a built-in speaker that provides better audio quality and considerably louder output, making it easier to hear spoken directions.
Basically, it doesn't seem like the TomTom device uses any hardware specific to the iPhone, meaning that it should work with the iPod Touch as well. If you are seriously considering using the iPhone / iPod Touch as your primary GPS device, it might be a good idea to look into the adapter when TomTom releases it sometime "later this summer." No pricing information has been released, but with accessories and the likelihood of monthly fees, I think I will be sticking to a dedicated device for now. [9 to 5 Mac]