Here are the step-by-step instructions to set up the Find My iPhone feature on the older iPhone and iPod Touch models.
Step 1: Download and install the free Find My iPhone application from the App Store on your iPhone 4, iPad or the new iPod Touch.
Step 2: If you have already set up a MobileMe account, skip this step. Otherwise, launch the application to create a new MobileMe account.
Step 3: From your iPhone Home Screen, navigate to Settings > Mail, Contacts, Calendars > Add a MobileMe account. Log in using your Apple ID and password.
Step 4: Once connected, turn the Find My iPhone feature on.
Step 5: Relaunch the Find My iPhone app and login using your credentials for the set up to be complete.
Step 6: These steps now need to be repeated for the older iDevices. Download the Find My iPhone app on your older iDevice and follow steps 3-5 to complete the set up.
Via : Lifehacker