iPhone 3Gs Voice Control lets you turn on and control necessary functions on your iPhone without using your hands. The Voice Control function, initiated by holding down the "Home" button for a few seconds, lets you make phone calls, play music, shuffle your playlist and more by saying the specific commands to initiate specific functions. However, as of April 2011 the Voice Control function is touchy; it can appear on your screen unexpectedly while the device is locked and begin playing music or calling people. While you cannot completely disable Voice Control, you can disable the function while the iPhone is locked to prevent it from turning on unexpectedly when you don't want it to.
Tap the "Settings" app on the iPhone home screen.
Select "Passcode Lock," and then enter your passcode if prompted.
Tap the "ON/OFF" toggle to the right of Voice Dial until "OFF" is highlighted.
Press the "Home" button just beneath the iPhone screen to return to the home screen.