DND should flash red

[IP PBX_Support]

UPDATE/SOLVED:
Got this working.

Pieces:
Yealink SIP-T28P with v71 (RPS firmware)
Asterisk 1.8.23.1 / FPBX 2.11

Set a PFK (button) (one of the ten on the right) as a BLF.
The code to enter is *76

Make sure FPBX has changed from the default FALSE to TRUE under 'Advanced Settings' for "Enable Device States"

Set a BLF on another phone for the above extension

It does not matter if the Yealink SIP-T28P has either phone or custom DND mode (in the phone's GUI)
I suggest you 'remove' the DND button all together (softkey).

When press the BLF, the light will go from GREEN to RED.
The BLF on the other phones will go from GREEN to RED.

I hope this helps.

Shawn