Plug the other two cords of the Plantronics APC-4 Hook Switch cable into the back of your Cisco phone into the HEADSET port and AUX port. Note: If you go to turn your CS55 headset on and you get a triple beep tone, follow the CS55 pairing guide. Note: Within your Cisco phone you may need to enable the hook switch mode by the steps below.
I have a large head and I struggle to find headsets that are comfortable for not only short time periods but more importantly - a full day. The Discover D722U is the most comfortable headset in years. I'm an Insurance Sales Manager and due to the pandemic - we are working remotely from home. That means lots of phone/talk time (5-6+ hours) and I have no complaints. They provide excellent noise-cancellation capabilities, soft cushions for your ears, and a flexible microphone.
I would certainly recommend this headset to friends and co-workers.