GROM Audio BTD in-Car Bluetooth Extension Dongle for Many Phones The BTD Dongle adapter allows the seamless Bluetooth integration for all vehicles supported with GROM Audio car integration kits. Allows for a wide set of functionality to be added: Bluetooth Hands free (HFP), Bluetooth Audio playback (A2DP), Bluetooth wireless audio control (AVRCP). In hands free mode you are able to: accept call, reject call, adjust audio volume - all using car stereo and steering wheel controls. Bluetooth Audio playback allows you to stream the music directly from your phone to the car stereo. Now you are able to listen to your MP3s or Pandora played from your mobile phone on car stereo. Bluetooth wireless audio control (AVRCP) allows you to forward or backward your music playback via car stereo/steering wheel controls.