Okay, I just joined this forum because it's the only place where I believe I can get help with the same question, but a slight tweak, that's been asked and answered several times.
I followed the instructions that bbox, who, obviously walks on water, provided. Now, a different issue. When using my headset I can hear the person on the other end just fine, but nobody on the other line can hear me. I hit 751+ a blank key + 05 + speaker. Lo and behold, I now just hit that no longer blank key and hear the dialtone through my headset! But since then I can make calls through the headset but even though I can hear the person on the other line that person can't hear me.
I thought it might be the headset so I tried two more. Same problem. I then hooked all three headsets to my old phone, and all worked fine. I could hear fine and so could the other person. I can't go back to my old phone because in order for the receptionist located upstairs to answer my phone, I have to use this type of phone, which must be the type that makes all that work. The phone is an NEC Dterm80.
It may or may not be relevant but I have noticed that while I'm speaking through my headset, when I turn the volume up and down the display that shows the volume going up and down reads "handset." Please, brilliant people, help me! I had fusion in my neck, but it didn't help my neck pain a whole lot. It just hurts like hell to talk on the phone even for a few minutes without without using a headset! Please, help! Thanks so much for everything y'all have already don for me. It's saved me countless hours of useless googling.