I find that the sound during voice calls is only average with callers complaining to me that my voice is muffled and gets cut off occasionally. Equally the voice of some callers gets cut off and it seems like there may be a problem with the mechanism (is it called VOX?) that switches on the microphone when I speak. I assume that mobile phones cannot actually have simultaneous 2-way talking, surely both parties cannot speak at the same time. My partner and I both have the same Galaxy W S8510 phones and Samsung say there is nothing wrong. Is this problem fixable ? Is sensitivty adjustable please ?