Phonelocator periodic is a free service to help you keep tabs on the location of your phone. It runs in the background and can periodically update the phone’s location to the Phonelocator server. You’ll need to sign up for an account at their site to track the location on your phone.
You can also designate a number to send a message to when the SIM card in your phone is changed. This will allow you to receive the number of the person who’s “borrowed” you phone.
This application can use GPS, Cell ID or Wifi to track the location of your phone. To get the latest location of the phone, all you need to do is to send a text message the phone which starts with the word Update, and the latest location of the phone gets updated on the PhoneLocator site.