I have full duplex (simultaneous audio recording & playback) working on 6630 when using the following settings for CMdaAudioOutputStream and CMdaAudioInputStream: (the information was posted on a public newsgroup discussion.epoc.c++, so this is not the information from forum nokia pro, which has been discussed in other topics)
1) CMdaAudioInputStream::NewL(*this, 99, TMdaPriorityPreference)0x1410001);
2) iOutputStream->SetPriority(80, (TMdaPriorityPreference)0x1310001);
But with those settings, audio interjection (playback to the audio uplink) during a voice call doesn't work. However, interjection works with setting prioritypreference of CMdaAudioOutputStream to (TMdaPriorityPreference)0x00060001 as stated earlier in this forum. But this breaks the full duplex functionality. Audio recording doesn't start at all.