No calls through car speakers with car dock, music ok..

[jte]

I have SGSII and Samsung Car Dock and all audio is running through usb to my car speakers and listening to music and navi works fine. However no phone calls are coming through my car speakers.
When making a call by default the speaker option is highlighted but this is going through the speaker on the back of the phone and not through the car speakers. In addition if I un-check the speaker option the call goes through the head piece on the phone.

Is this a feature or do I something wrong?

[greenman]

Would think you have to connect phone audio via the headphone socket.

[Dannyboy]

Thats how I do it and it works fine.