A:
It only partially supports HSP. I found this out because I ordered a Panasonic telephone that was HSP compatible, but I could never get it to connect to my H800. I contacted Logitech support tonight, and they said that it supports HSP, but ONLY for a select few devices. So really its a hit-or-miss on whether or not this unit will support your HSP device.
To be clear, I have two H800s and I TOTALLY LOVE THEM and use them 20-30 hours a week for my conference calls (work from home.) The fit is great, the audio is great, I love the volume control buttons and mute button, and I often switch between my PC (USB dongle) and phone (bluetooth), and so I absolutely love this product; I'm just disappointed that I tried connecting it to a landline phone that is HSP compatible, just to find that the H800 wouldn't connect.