I have the Parrot CK3000 Evolution which is completely hidden in the interior light cluster. I also have the multi-can so it works via the phone button on the MFSW and through the car speakers, muting the stereo if I have a call.
The only part of it on display is the microphone which is located at the top of the A pillar (it was in the light cluster to start with but my callers couldn't hear me as it made me sound muffled).
It works with voicetags, so your phone has to have this feature for it to work. I was also advised to have the bluetooth switched on on my phone before I turn the ignition on otherwise it might not work properly. I leave my bluetooth on all the time so I don't have to remember to turn it on before getting in the car.
I have a Nokia 6500s and have had no issues with it whatsoever.