Mine was exactly the same as yours. I think you described it perfectly, it's like holding a shell to your ear. In fact there were times, I made a call, and didn't even bother holding it to my ear and I could still hear the person on the other end.
I don't have the Orbit anymore, got the Trinity instead, and I think call quality on the Trinity is much better.
You can try swapping it for another one, as you have 28 days. Maybe both of us were unlucky.
I don't think you can adjust the sound qaulity for the call. Someone correct me if I'm wrong.