Need plantronics adaptor for logitech usb headset

[Jewels2500]

My job uses old fashioned plantronics headsets that plug into the back of the phone. I own a nice logitech usb headset and need an adaptor to connect the usb to the phone. Any ideas on where to find something like this or what it's even called? Thanks.

 

[Alabalcho]

Not an easy task... USB is digital interface, so what you're looking for is actually a computer with analog line-in (from the phone), analog output (to the phone), and USB connector (with drivers) where to plug your Logitech headset, with piece of software to translate between them.