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Okay I'm missing something. I have a $50 motorola bluetooth speakerphone in my car. All I have to do is tap the Motorola's "call" button and Siri is activated. It doesn't work that way with built-in car systems?

Apparently not. I have a Motorola headset too, its nice just touching the button on it and hear Siri answer.
 
Works fine with my BlueAnt Bluetooth headset too.

Just tap the main button on the headset & Siri is ready to help.
 
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