I use a Plantronics CS55 with the HL/10 lifter at my desk. I'm not sure what you are asking in reference to high call volume, but with the lifter you can control the hookswitch from the button on the headset, and wouldn't need a headset key on the phone. Actually, it wouldn't do much good anyway, because the unit is connected in line with the handset, not plugged into the headset jack.

I untilize call waiting, flash between callers if needed, and use virtual answer (everyone thinks that is cool!) during high call volumes.

Headsets aside, we've also made ACD groups with only one agent in them to handle users with high call volumes.

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