iPhone 3gs and iPhone 4 voice control allows you to make phone calls and control iPod music playback using voice commands. In order to use Voice Control – Press and hold the Home button until the Voice Control screen appears and you hear a beep or else You can also press and hold the center button on the iPhone earphones.
Use Following Commands To Make Calls
Call someone in contacts – Say “call” or “dial,” then say the name of person. If the person has more than one number, you can add “home” or “mobile”
Dial a number – Say “call” or “dial,” then say the number