I don't want to muddy the waters on this one but I wanted to mention some things that have happened to me with several phones over the last few years. Thunderbolt....BT headset needed to be replaced as it had no outgoing voice but could hear people fine. Rezound.... BT headset (plantronics I believe) wouldn't even connect to the phone, replaced with a jawbone. Wife's Inc 4g... needed a new BT headset (had an older jawbone, replaced with a newer one) it would connect to the phone and work most of the time, but sporadically it would have no sound or voice communication at all.
All of these headsets were tested on both the older phones and the newer ones when the issues were occurring. The headsets would work without any issues on the older phones, but the new ones just wouldn't work correctly.
I'm not sure if it was just a bluetooth version incompatibility (they seem to update the BT version with every damn phone) or extremely bad luck, but the problems were occurring and could be duplicated consistently. I know they say BT is backwards compatible, but I've seen issues over the years.