The noise cancellation feature on the Nexus One is great. The phone has two microphones; one is at the bottom of the phone and the other on the back. How this works?
The microphone on the back cancels out inbound noise so you hear only the callers' voice. The callers also get a good quality call experience. I experienced that yesterday when I got stuck on M1 and calling my brother he did not hear the heavy traffic noise around me, nor did I hear anything on his side but his voice. This is a feature that should be made standard on all phones.
The Nexus One phone experience is not so different from other phones I've used, except for the loudspeaker. It's just not loud enough and you have to hold the phone somehow close to hear the caller. This same feature on the Touch Pro2 is excellent.