Electronic Hook Switch (phone interface)

Our office has just changed to a Panasonic phone system.

the phone is a KX-DT543

I have a Plantronics CS55 wireless headset.

the phone has an EHS or electronic hook switch port, looks like a stereo plug for 1/8" dia connector.

Plantronics is clueless although they have interfaces for multiple other phone manufacturers.

Does anyone have any experience or technical information about the interface ?

My Panasonic has a headset connector, which is a 2.5mm jack with 3 segments (ground, mic, mono phones). As far as I know, the EHS requires an extra wire to pick up the phone. So I think it could be a 2.5mm jack with 4 segments.

risking one of the new $350 phones, we plugged in a male/male headphone jack.

the plantronics closes a relay internally. this is connected to the EHS port on the phone.

the phone 'lifts' the handset, but leaves the hand piece in place and activates the speaker and mic on the handset.

the plantronics interupts these siganl (you plug the plantronics into the phone base and the handset into the plantronics. in normal phone mode, the plantronics is a pass-through.

with the EHS operating the plantronics wirelss is working.

simple as a patch cord.