1. Update the iTunes software on your PC or Mac to the latest version. 2. If your iPhone3G (iPhone3GS comes with 3.0 installed) is not yet running OS 3.0 software (tap "Settings" from the home screen, then "General" then "About" - see version), sync your iPhone to iTunes to upgrade. 3. After the upgrade, turn off your iPhone, then re-start and tap "Settings." 4. Tap "Mail, Contacts, and Calendars." 5. Be sure "Fetch New Data" is set to "Push." 6. Open your MobileMe account on your PC or Mac, and turn on "Find my iPhone." 7. Follow instructions to locate, chime, and/or message your lost iPhone. Tips: 1. You must have a subscription to MobileMe to use the Find my iPhone service. What You Need: * iPhone3G or iPhone3GS running OS 3.0 * Subscription to MobileMe (see links below) * Latest version of iTunes installed and running on your PC or Mac