An iPhone's voice control tool dials numbers by matching your voice with the names of contacts stored in your phone, or based on a number you speak into the phone. By configuring the phone's passcode tool, you can disable the voice dialling feature when the phone is locked and prevent accidental calls.
Touch "Settings" and "General" on the phone's screen.
Tap "Passcode Lock" and "Turn Passcode On." Enter the passcode twice to activate the passcode lock.
Touch the switch on the "Voice Dial" tab to disable it.
The voice control tool for the phone's iPod application cannot be disabled. This tool activates when the iPhone's home button is held down for several seconds. To prevent accidentally activating the tool, avoid holding down the home button and try not to keep the phone in a pocket or other confined space where the button could be inadvertently pressed.