My car kit works by bluetooth, so any phone with bluetooth works with it. I imagine that it is the kit rather than the phone is the key factor to the quality.
Mine works pretty well, though is sometimes has a bit of an echo, especially when talking to someone else on their car kit.
I got one for about £7. It broke in a couple of days and blew the fuse in my cigarette lighter. I've just got the tomtom one (and I got the application on my phone). The carkit cost £100, but works perfectly, has a speaker and microphone for handsfree calls, and its own gps so it doesn't cost me a fortune to use tomtom abroad (I'm in the netherlands right now). So in my experience you get what you pay for.