samclarke,
You my friend on in the wrong forum. This is a screenshot of a 3300 not a MiVO-250. I will get you over to that forum to get the correct answer.
Unfortunately those feature codes are programmable and I haven't seen it done the same way twice yet and different technicians use different defaults for that; sorry.
You are in the correct locations by the way for feature codes, but I don't think there is one for headsets; at least not on the 6900 series phones which is all I have seen on the 3300 so far.
Thanks,
TE