UPDATE: Apple apparently only allows you to setup 3 accounts from your iPhone 4. The accounts are registered via your iPhone's serial number. Once you have registered 3 accounts, you will not be able to setup any more accounts from your iPhone 4. To date, there is no way to reverse the limit, should you reach it. Be warned, people! Ok, so Apple released Find my iPhone as a free feature for the iPhone 4 today - along with iOS 4.2. It's a great feature, and allows you to use a GPS web app to track your devices (should you lose your phone in a park, for instance). Any iPhone you own can have access to the Find my iPhone packaged with MobileMe (Apple's pay service). With this tutorial you can setup unique Find my iPhone accounts for your older iOS devices - presuming you don't want to track all of your older devices from the same MobileMe account. From your iPhone 4: 1. The phone will need to be updated to iOS 4.2 2. Download 'Find my iPhone' app from the App Store (free). 3. Go to Settings> Mail, Contacts, Calendars > Add Account...> MobileMe> 4. At the MobileMe login menu, input the Apple ID you want to setup on the older device: 5. Press Next to setup the account. 6. Click the link in Apple's verification email. 7. You should now see your account on the new iPhone (in the settings menu). 8. Do NOT turn on Find my iPhone from your iPhone 4 (if you have MobileMe, doing so will override your current Find my iPhone, though it can be turned back on later). From your older iPhone/iOS device! 1. Go to Settings> Mail, Contacts, Calendars > Add Account...> MobileMe> 2. At the MobileMe login menu, input your AppleID and password (the same account you use to log into and download apps from the App Store). 3. Press Next to setup the account. 4. You should now see your account on your older iPhone/iOS device (in the settings menu). 5. Download 'Find my iPhone' app. 6. Open Find my iPhone app on your iPhone. 7. Input the same Apple ID and password you used before. Your iPhone 3G/3GS has now been added to your new Find my iPhone account. The last step is to delete your login information from your iPhone 4, just to make sure that they don't ever conflict. You can now login to your account at http://me.com using your ID and password, and you will be able to track your 3G/3GS!