Thank you dos, for the confirmation and link to the issue report. The issue report gives me enough to be able to test the hardware on the phone.
And although it doesn’t have the convenience of auto detect and switching, I can at least set the phone up to make use of the headset microphone.
Edit: To give some additional detail to this, the i2ctransfer writes only work for me when the headset is disconnected from the phone (Evergreen/amber-phone). With the headset plugged in the i2ctransfer writes silently fail or don’t take.
I was slightly disconcerted by the note regarding the -f flag from the man pages which reads " It can also cause i2ctransfer to silently write to the wrong register." @dos Have you experienced any problems or issues in this area?