Since the disappointment of the Dension Gateway 100 not charging the iPhone 3G I have been seeking answers as to what the problem is and it appears that Apple have removed the ability to charge the iPhone 3G via Firewire. The iPods and original iPhone connector has two sets of power connectors - one for USB and one for Firewire but the new iPhone 3G only has USB charging pins.

Apple decided to completely remove support for Firewire charging on the iPhone 3G, therefore certain accessories will not charge the iPhone 3G. Not all of them are incompatible with the iPhone 3G when it comes to charging. Only those that were designed with the Firewire charging ports. Unfortunately because of the difference in voltages, 5V for USB and 12V for Firewire and cars operating in the 12 Volt range, every wired car kit uses the 12 volt Firewire option to avoid changing voltages, this is why they do not work.