As far as I remember, in order for the N900 to pick up radio transmission, it has to have the headphones connected - no? So, in order for this idea to work, you'll have to first connect the headphones to the N900, allow it to scan frequencies and do his thing (find an "empty" frequency), and then disconnect the headphones and activate the FM transmitter... Do you ALWAYS drive your car with your headphones somewhere with you? because if you don't, you can't use this type of function... In addition, as far as I know the N900 RECEIVER is significantly less capable than an ordinary car's receiver, so normally stations that will be picked easily by your car's radio will not be picked as much as easily (or even - not at all) with your N900. Nevertheless - don't get me wrong, the idea is very nice but I'm not quite sure how practical it is...