Voice dial without wifi

[AC Question]

many years ago mobile phones could dial a number by recognising a voice command. This was long before wifi. How can this be achieved on a Sony Xperia z3 compact without wifi please (while phone connected to a bluetooth headset) - I have a call plan, I am not trying to avoid costs nor use IP phone - I just want the phone to respond to voice and dial a number. Would this need some form of physical prompt on either the phone or the headset for the phone to respond?