There are two types of headsets available for NEC Phones.
The newer model NEC Phones include a headset jack to add a headset. A headset can simply plug into the phone, the phone can be programmed into headset mode, and away you go.
The new model phones that do include a headset jack are the Electra Elite, Aspire, DSX, SL1100, SV8100, SV9100, and the UX5000 phone systems.
The headsets that include "DC" at the end of the title are the headsets compatible the newer model NEC phones that include a headset jack.
The older model NEC phones do not include a jack for a headset, there for an amplifier is required plus the headset.
The older model phone systems that a headset will work well with that will require an amplifier are the: DS1000, DS2000, and the I Series phone systems.