The audio adapter is designed for the HTC One X Plus:
HTC One X Plus
If you prefer to use a 2.5mm headset with your HTC One X Plus cell phone, you will need to plug in the 2.5mm audio adapter in order for the headset to work. Just plug this audio adapter into your cell phone to convert the audio. This adapter allows you to use a 2.5 headset with your HTC One X Plus phone.
Easily installs; simply plug the audio adapter into your HTC One X Plus cell phone audio jack; then plug in any 2.5mm, two ring headset into the audio adapter
Currently offered on: AT&T
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Original HTC One X Plus Hands Free 2.5 Audio Adapter