I thow the 400 series has headset ports under them. I have had a bunch of the 500 series but never rolled them out before Iwent to the 4K. I believe for those you have to buy the headset module that plugs into the bottom of them and that does not require a lifter. If you are using Plantronics headsets the cord you need to use for the 400 series is P/N 66268-03 and AKA A10-16-S1
Don Bruechert, Voice Comm Analyst II
CareTech Solutions @ Holy Family Memorial
Manitowoc, WI, USA