If you really want double din detachable faceplate stereo, and you haven't picked one up yet, check out the Sony XAV-601BT (about $550). I've had it for a little over two months now and I really like it. I also wanted a double din with a detachable faceplate and I almost went with a JVC. I'm glad I chose this Sony because it has everything i was looking for. In the past I avoided Sony's car audio stuff because it always looked cheap and cheesy. But on this deck, it looks great and I really like the interface and menus over all of the JVCs, Pioneers, Kenwoods, etc. (but that's obviously just my preference)
I don't use navigation so I can't give specifics about the navigation, but I can say that you can play music from your iPhone while using the navigation. There are even built-in controls for music in the navigation app. The navigation is run from a free iPhone app called TeleNav GPS. So no, it doesn't have navigation built in, but it is a free app you can try out even before buying the deck. If I remember correctly, there's a TomTom thing you can add on for full nav, but that'll set you back two or three hundred dollars. And that could be overkill if you're just looking for point A to B navigation.
The reviews on Amazon
and Crutchfield aren't that great because it seems like quite a few people bought it without even doing much research on and were expecting the unit to basically mirror their iPhone's screen, which it doesn't do. So don't look at the relatively low score on Amazon or Crutchfield and dismiss this awesome deck. If you have any questions or want pictures of how it looks in a second gen I'd be happy to help. Just hit me up!