Echo when using headset on T46S and T42G

[IZT-crobinson]

Hello,

I have a plantronics C054 headset and I am getting echo in whatever the caller is saying. I contacted the seller of the headset and told them it was defective, so they send me another one, and I have the same issue. I tried lowering the volume and everything. I tried the switch on the bottom and I either get a combonation of these:

1) Can't hear dialtone
2) Can't hear caller
3) Caller can't hear me

All I want is this to work, but now I am thinking it might be the phones themselves.

Any help is much appreciated.