Take the "intelligent" car key, a wireless fob which allows unlocking your car and starting the engine by simple proximity to the vehicle. Build that functionality into a mobile phone. That's the innovative gadget convergence which Nissan, NTT Docomo and Sharp, stumped for a catchy name, have dubbed "Mobile Phone with Intelligent Key". As long as you've got your phone with you, the open road belongs to you and your Nissan. Simple as that. The companies are rushing to put the concept into production.
More info (Japanese):
http://tiny.cc/6x1SU