My Blackberry Flip 8220 has developed this flaw. Any bluetooth headset (I have tried two of them) is always muted. I can hear the caller through the headset but no sound is picked up my the headset. The headsets work fine with other phones.
The BB Flip is running 4.6.180. I have tried the usual, disconnecting the battery, reseat the SIM card (Though not relevant to my case) etc.
