Mic location doesn't really matter much... at least in my case it doesn't matter. I've tried 5 or 6 different locations in my 2009 VW GTI and there was no notable difference.
I have an iPhone 4 with iOS 4.1, and the Bluetooth use on my AVIC-Z120 is shit. It pisses me off, beyond belief that I dropped $1,000+ on a HU and can't use the Bluetooth.
I've read that Apple's implementation of the Bluetooth protocol is piss-poor, so I paired my friends HTC (Android) and placed a test call. While I wasn't on the receiving end of the call, my caller said there was a marked improvement over my iPh