Route in-call audio to A2DP headset How can I set up my Nexus 4 to receive Hangouts and phone call audio over a Bluetooth A2DP link? Even though my headphones are connected, in-call audio is routed to the earpiece or speaker and there's no option to send it over BT.

I've got Creative WP-350 headphones that support both A2DP and HSP but the headset profile audio quality is unusably low, leaving no other option but to disable it in Android BT settings.
Unfortunately A2DP supports only stereo audio, it doesn't support two-way audio, i.e. your mic woud be useless if the calls were routed over A2DP. You'll have to enable HSP for call functionality.