Ridax, they make various Dock connectors for the iPhone has started taking pre-orders for its iPhone 3G Charge converter, which may be of interest to you as although the 30 pin Dock connector in the iPhone 3G looks the same as the 2G iPod is doesn’t actually support charging the old Firewire charging pin.
Looking at a report on ilounge, this means of course that there are a host of old charger and Docks that won’t work with the new iPhone 3G. However, this is where Ridax steps in with their new Dock connector, although the design is still being finished.
Hopefully other manufacturers of Dock connectors won’t take the same path as Ridax though and charge a huge $40.00 for two resistors and connectors as Ridax does.
So if you are that desperate or impatient enough to bung $40.00 on this dock connector you should be able to charge via the built-in mini-USB located on its side.
However, if you can wait I’m sure more affordable dock connectors will be hitting the streets by the time Ridax ships there’s sometime in September.
US-based CableJive has a charge converter for iPhone 3G and newer iPods
http://cablejive.com/iphone_3g_charge_converter.html