The Plantronics MDA200 (MDA220) is a product that not many folks seem to know about, however, in many cases, it’s the exact thing you need.
It’s a very versatile product that allows multi-connectivity to desk phones and PCs. You may say there are tons of products that do this. You are correct. What makes the MDA200 special is that you can take a USB headset and use it with your desk phone (and PC). You can use a Blackwire USB headset or a Plantronics QD headset and DA USB adapter.