Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: Just making sure it does not require any other adapter to work -- I can plug into the jack on back side of Avaya 9620 and press headset to work
Document: I hated the headset I was provided at work and so I started doing a little research and took a leap of faith here. It is wonderful. Very comfortable. I love the adjustable microphone. I am actully getting ready to order 30 more for my employees to replace the $200 headsets we were provided.- Using with AVAYA 9608. you have to plug it into the handset jack and simply take the phone off the hook to answer the phone. This save having to buy the $70 amplifier. *win
Tried on Avaya 4412D+ and 4424D+. Can hear the person at the other end, but that person can hear nothing. The seller promptly sent a second headset that did not work either.
These headphones work perfectly with my Avaya 2410 phone. Very clear and so comfortable that I forget I have them on my head!
Works great but the volume knob crackles when making adjustments. Item looks cheap, but is very lightweight. If plantronics made it, it would probably be allot better. I use mine for/at work.
In an office setting, you're typically limited to very expensive headsets. Prior to finding this one, I would've considered anything under $100 a bargain. But I discovered these for around $20, and decided to give it a try.They come bare bones in a plastic ziplock bag, no fancy packaging. What you'll find inside is the headset and cord. It plugs right into your office phone, assuming it is one of the supported units (in my case Avaya).
With my new office IP telephone - an Avaya 4610SW IP model - the $20 Call Center Headset does what it should - frees up the hands. Altering the position of the microphone changes the loudness of my voice. The headphone has its own volume control: a small wheel built into the cord.
The call center I work for supplied my headset but a short developed in the cord and they wouldnt replace. This headset is cheap and the microphone is flexible. Good product for the price
I work in a small office that occassionally needs to make hundreds of calls in a week to recruit people for our advocacy work. I found this headset on Amazon after a lot of careful research. Works great with our AVAYA 4412D+ telephones. Because they're not the same brand as my phone there is a trick to them as they work in the handset input rather than the headset input. Other than that they handled the job very well.
Much better is simply to have an uncoiled cord. (b) The mute button switch is fiddly and stiff - it is made of smooth plastic and sits in a U-shaped channel. A better design would give it a knobbly texture and have it protrude a bit. Overall, this headset is much cheaper than the official Avaya equivalent and allows hands-free telephony. With a couple of simple design improvements, it would warrant five stars.
It worked well for a while but then kinda crapped out. Not sure if it was the product or the receptionist's fault.
Answer: You can connect it and talk/listen using the headset but you still need the handset to open/close the call.  So it is not a "full" solution.