I have played around some with uploading custom ringtones just to test the feature.
I have found a bud with incomming calls to cordless Plantronics headsets when using uploaded custom ringtones. There is no outbound audio. Inbound audio works fine. For purely outbound calls the audio seems to be working normally. I have played around with different settings but from what I can tell the only soloution is to remove the custom ringtone if you want the Plantronics cordless headset to work. I have not tried this with other brands so it may or may not be limited to Plantronics headsets.
Not a major bug but a bug nonetheless