Paul Thurrott has shown off the specifics of MS’s Find My Phone that is going to be a free service from MS with WP7. These are tools t o help you locate a missing or stolen phone. It comes bundled with four services. The first is to map it (using Bing obviously), second is to have your phone ring for 60 seconds using a special ringtone (that overrides your phone being set to silent), third is the ability to lock your phone and display a message on how to return your phone (setting a new 4 digit code to unlock it) and finally you can erase all of your info from the phone (returning it to factory settings).
Head over to his blog to see each of these actions in details