I originally bought this cable to connect a Plantronics headset to the headset port on my Grandstream GXP1450. detail number. What isn't clear in the manual is that they also refer to another passive adapter that needs to be used along with the cable to work properly. In short, I decided that the headset would not work properly with just the cable as the polarity of the microphone was reversed. Physically removing the RJ9 connector and inserting a new connector rotated 180 degrees (upside down) resolved the polarity issue and the headset is working properly. Since Plantronics sells at least 4 variants of this cable, it is unclear if there is a better one. really more suitable for this application. Anyway, I hope this helps the other unlucky person who read the Grandstream Compatibility Guide and doesn't want to spend another $20 on another passive adapter.
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