The audio adapter is designed for the Kyocera Coast:
Kyocera Coast
If you prefer to use a 2.5mm headset with your Kyocera Coast 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 Kyocera Coast phone.
Easily installs; simply plug the audio adapter into your Kyocera Coast cell phone audio jack; then plug in any 2.5mm, two ring headset into the audio adapter
Currently offered on: Boost, Cricket and Virgin
All carriers including Alltel/ AT&T/ Sprint PCS/ T-Mobile and Verizon are trademarks of the respective companies
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Original Kyocera Coast Hands Free 2.5 Audio Adapter