Find my phone is an online service for Windows Phone 7 users to locate their phone in case on theft or loss:
- To enable this option on your phone:
- From the Home screen >Settings > System > Find my Phone
- Select "Save my location periodically for better mapping".
From there you can access :
http://windowsphone.live.com/
Sign-in with your Windows Live ID and perform one of the following action
- Map it:locate your phone on a map
- Ring it: rings your phone
- Lock it: locks your phone
- Erase it: Reset to factory settings and delete your private data