How can I use my iPad with a Bluetooth headset or hands-free?

I'm looking to ditch my iPhone for my iPad. Apps I've tried are: Skype, Google Voice, Talkatone & Whisper. I've solved the incoming call problem, all that remains is the Bluetooth hurdle. When connected via my car's (Scion xB) bluetooth connection it pauses the music that is currently playing, but no audio from the call is received, nor is the car's microphone being used. I'd love to hear your story on how you're using an iPad as a phone if you have one as well.