T48G Problems with old Plantronics Headset

[Lazzard]

Hi Guys,

I got a T48G a few days ago. I tried to connect my old Plantronics wired call center headset to the phone using RJ9. I can hear the caller, but he can't hear me. Is it possible that the pins are assigned differently?

I tried a Yealink headset, it works on the phone. But the quality is not so good.

My old headset works because I used it on my old phone without any problems.

Anybody got any ideas?