I have had an AVIC-D3 for a couple of months now and I can confirm that the Bluetooth adapter does work with the iPhone. However, here's a couple of things you need to know:
1. You will have to manually connect your phone if you want to place calls through the head unit. There is an option on the D3 to have the head unit autoconnect to a phone, but it doesn't work with the iPhone (it didn't work with my Windows Mobile phone either, by the way). Make sure you go to the Direct Connect screen after you pair the iPhone and press and hold one of the items in the list. This will create an entry for the iPhone that you can use to direct connect in the future. A surprising feature is if you have not connected your phone and your receive a call, your iPhone will connect to the D3 when the call comes in. The same thing happened with my Windows Mobile phone.
2. I have not found a way to transmit the iPhone contacts to the head unit. This is pretty annoying since my Windows Mobile phone did this, although I did have to install some extra software to do it. This means, if you want to use the head unit to place a call, you will either have to dial the number manually or use the iPhone to dial.
Hope this helps.
Chris
P.S. If there's anything else you need to know about the D3, feel free to let me know.