Well, if your car was purchased in England (or perhaps other parts of Europe), you might be able to do so -- most cars there use IR instead of RF. People have been using OmniRemote to unlock their cars there (along with passers-by stealing the IR codes)

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If you haven't already, please vote on a bluetooth voice AND data adapter for the 7135 (that plugs into the serial port, leaving your expansion card slot free!)