Registered here to add to the discussion. I just recently purchased an HTC One X+ and immediately ran into this bluetooth issue you all describe. Phone call quality was horrible on 4 different bluetooth sets: Voyager 520(2), Voyager Pro, and the Jawbone Prime all had an awful, horrible sound which made it impossible for me to use the phone.
By your suggestion, I purchased a blueant Q2 today and am now enjoying clear call quality. The salesman at the AT&T store mentioned that the bluetooth 4.0 technology is giving people problems across the spectrum. iPhone 5 users are apparently reporting problems as well he said.
I, however can not attest to this. I did notice that the Beats Audio is now enabled with the new blueant Q2 headset. With the other earpieces, Beats was disabled and could not be used with the device (grayed out). This may be the problem.
Any thoughts? Or is this thread dead?