There are a few couples here in Nor Cal that are using the Nolan N-Com helmets.
My wife and I (riding seperate bikes) use them. We ride Street Glides (09 and 10) so we don't have the same HK as the Ultra Classics. Neither do we have the 660/665 but the older Garmin 2730 Streetpilots.
It's true, you can be listening to your stereo in the helmet and when you receive a call, just press the button on the side of your helmet to take the call. It will cancel out the stereo until you disconnect the phone and reconnect to the stereo.
You can not be on the intercom and listening to your stereo through the helmet speakers at the same time. However, you can be on the intercom system and then click over to take a call.
The other thing that's pretty surprising is that it cancels out all background noise when you're on the phone. At 80 mph on the freeway nobody will believe that you're on your bike talking on the phone. It's that quiet and that clear.