A friend bought a 10c so we could both record video when we ride, I have had one for a year and he had the SPH10H. So I get his new 10c installed into his helmet and we get to trying to pair our 10c's. No problem connected right away, he could hear me, but I could not hear him. We tried again with the SPH10H, same thing, could not hear him. I was thinking the boom mic was bad so I put in the wired mic, same issue! Let the troubleshooting begin, here is what I tried....

Reset to factory default
Firmware 2.0
Recorded a test video (MIC works)
Recorded a video while connected to another 10c (MIC works in the video, but could not hear him in the other 10c)
Took his 10c and swapped with mine (his unit worked fine in my helmet, my 10c in his helmet had the issue)
Used his 10c in my helmet to connect to the SPH10H and everything worked fine.

It appears to be something in the Speaker/mic kit. Rather than deal with RMA'ing the whole package, he has ordered a replacement speaker/mic kit. I will update this thread with the results. Fingers crossed!