This set is a NEC Electra Elite DTU-16D-2 (BK) and has both a "handset" and "headset" jack. The pamphlet says that one can use a headset in the headset jack by pressing the "headset button" on the set. But I can find no such button.
What am I missing here? If one of the soft keys needs to be programmed as a "headset" button, can anyone describe how to do this? The pamphlet says nothing about it, and the system programming manual is gone, nach.