It's possible to set commands on many different languages so this feature is quite multicultural. To set a language you must go to Settings > General > International > Voice Control.
Then you have to navigate to your contacts within your phone, then slide a finger along right side on the contact you want to call, tap the contact's name and then the desired phone number.
If you have your iphone in the pocket carrying headsets, you can just hold down the middle button until the voice command announces, say a command and then wait for the confirmation what means that the phone started to implement the operation.
It’s either convenient for those who have troubles with using their iphones touch as well as for blinds and disables.