Q:
Do not understand how you can say the HL10 works with the M22 amp when in fact there is no socket on the M22 to plug in the HL10. I ended up buying it and then returning it. I found a Plantronics S20 amp which works really great and does support the HL10. But if I was unable to get that S20, I would probably get the Plantronics headset integrated with a phone as my second choice for a wired solution (I really don't want a battery headset because I am on the phone all day and batteries won't last). Just use a duplex plug to connect inline as it has no handset, so you don't need a lifter.
If you are going to answer technical questions you need to know what you are doing.