A question about the beginning of car radios

The good folks in the Vintage Chevrolet Club of America are wondering, what was the beginning of radios being used in cars?

The answer appears to be 1922 or '23.
http://vccachat.org/forum/ubbthreads.php/ubb/showflat/Number/130795/gonew/1

There is a slightly different question, When was the first commercially available radio, factory installed as an option?
The answer is 1927, Philco radio.
http://www.answerbag.com/q_view/78829