The night-service code *800 command (under telephony-service) lets you manually enter a code to enable/disable the night mode.
Dialling the same code again re-enables it.
However, if you do this, how do you know whether it's currently enabled or not? Can you set a BLF-type button or get a special tone to determine whether the system currently has night service active?
Well, I guess this was a bit of a silly question because the phones displays "Night Service Active" as the status.
However, if DND is active, the DND message takes precedence, so I couldn't see that message.
The BLF-style light would still be nice but at least it's usable.