i tested this with a friend and fortunately. the mic on the n900 works quite well and he cannot detect any echo in his voice. he also says there is no discernible difference between this and hearing me with the phone held near my face..and this is with the n900 held at a distance of about 12" from my mouth. not too bad indeed!

i also like the fact that with the car radio, i can boost up the audio to levels beyond any bluetooth headset or built in speaker can.