People misplace things all the time. Fortunately, if you lose your iPhone, Apple’s “Find My iPhone” app can help. It’s easy to activate this feature on your iPhone, all it takes is a few easy steps.
First step is to make sure you have operating system 3.0 or higher installed. To do this, connect your iPhone to your computer and follow the onscreen instructions in iTunes.
Next, click Settings on your iPhone, tap iCloud, and click setup. Once iCloud is set up, you will see an option to turn “Find My iPhone” on or off. Make sure this switch is toggled to “on”.
Then if you misplace your iPhone, you can sign in to icloud.com with your apple user ID and password from any computer web browser or iPhone to lock the phone, play an alert and display its approximate location on a map.
For more info: http://www.apple.com/icloud/setup/
Link to Find My iPhone App: http://itunes.apple.com/us/app/find-my-iphone/id376101648?mt=8