You can't.
I was at a Genius Bar appointment today for something else and asked. Nope. You have to touch the iPhone to get Siri to work. I'd rather have hands free dialing (well, touch the ear bud) so no Siri for me. Maybe I'll play with that function in my idle hours just to see how it works.
With my Plantronics M50, I just long click the ear bud and say "Call XYZ" or "Dial 123" or double click it and it redials. THAT is useful.
I was at a Genius Bar appointment today for something else and asked. Nope. You have to touch the iPhone to get Siri to work. I'd rather have hands free dialing (well, touch the ear bud) so no Siri for me. Maybe I'll play with that function in my idle hours just to see how it works.
With my Plantronics M50, I just long click the ear bud and say "Call XYZ" or "Dial 123" or double click it and it redials. THAT is useful.