I've had good luck with the Jabra GN2100 headset, and GN1200 cord. The cord has an 8-position slide switch inline with it that will match the pinout/mic gain to work with pretty much anything. (Nortel M and T series, Nortel/Avaya IP, Cisco IP, Panasonic, NEC, Ascom, Philips, and Plantronics amps.)

https://img8.jabra.com/sites/Jabra/...ments/Datasheet/GN1200_DS_AP_US_1045.pdf

The headset itself is clear and (in my opinion) comfortable, and they aren't horrendously expensive.


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- Adam