I am having that problem with the Note II also. I just got a replacement phone because I reported it to Best Buy where I bought the phone, and they replaced the phone, and it was fine the first night, but the next day (today) I cannot make calls at all - the call connects, and the other person answers, but I cannot hear them and they cannot hear me. What was happening before is that I would be on a call, and all of a sudden, it would stop sending sound. The person on the other line would start saying, "Lynne, hello, are you there?". Then, if I tried to call them back, I would get the no hear/no hear result. If I then restarted the phone, I could get the sound back, but it would happen again - some times 3 or 4 times on a call. This happened in the car, but at home too, so I don't think it's phone or network related because the network should have been stable when you are sitting in one place, right? And now I've ruled out a lemon phone because the new one is doing it even worse - I cannot even get it to work after a restart.
I saw some other posts on this on Sprint (my carrier), and it seems like there is no clear answer to why this is happening, but I'm basically screwed without a phone. I had a different Samsung phone before this, and I never had this problem ever not once.