Bluetooth phone question

My car has got the "on dash" phone kit however I haven't got the phone cradle yet. The phone works fine with bluetooth coming through the stereo but I cannot work out how to answer the incoming calls except for pressing the button on the phone its self which then cuts out bluetooth. Im sure there is a button on the dash somewhere I can press!

As far as I can see there is not mention in the instruction book about this???

I'm not sure which kit it is other than it's the one that is fixed to the side of the stereo and needs an adapter plate to work properly I think. Having said this, I can make a call from the phone and the sound comes through the stereo but I cannot accept incoming calls as it switches to the phones speaker when I answer it.