Comment 48 for bug 1576559

For those approaching the issue from afresh it looks like HSP/HFP shares functionality with bluetooth modems rather than solely audio. As such there's a disagreement between pulseaudio who are only interested in the audio parts, ofono who deals with the modem parts and the bluetooth stack (bluez) who connect the to the hardware.

The issue came about as support was dropped (assuming someone else would pick it up) as pulse audio and bluez went to later versions. It hasn't been resolved because no one wants to ether deal with the other part, or have another abstraction layer to switch between modem and audio functionality