I have been trying to get a known-working headset working on the headset jack on a 24 button phone. I have set the mode to both and headset and turned on headset = no go. I cut off a headset connector, plugged into the phone and used a cable tracer to check for any audio - nothing! HELP!

Using a Headset with a 2.5 mm Headset Jack (Ear/Mic)
If you are using a special headset that has a 2.5mm headset jack, (that is
Ear/Mic units) a special setting in addition to the basic Headset Mode setting
is required.

Follow the steps 1 through 6 for Setting the Headset Mode.
7. Use on the Nav Button to
access the Programming
Menu.
8. Use on the Nav Button to
scroll to the ADVANCED
PROGRAM option.
9. Press the OK soft button to
select the ADVANCED
PROGRAM option.
10. Use on the Nav button to scroll through the options.
When you see the EAR/MIC PROGRAM option:
11. Press the OK soft button to
select the option.

That got the headset ear working! The headset I'm using must not be proper impedance - getting "feedback". Oh well. Hope retirement is all you hoped for.