Just a follow up from my last post. The "Find My Phone" feature is a premium service of My Phone (My Phone itself is free). But there is also a 7 day trial. Note that there are more options that I originally mentioned. You can:
1. Ring the phone (even if the phone is in vibrate or silent mode)
2. Locate the phone on a map (last synch location is part of the free service, current location is a premium service)
3. Lock the phone (and leave a message indicating how to contact you)
4. Erase the phone (reset to factory defaults)
The 7 day trial allows you to try 3 each of the first two options and 1 each of the last two. So far, the 2nd option (locate my phone) hasn't worked for me. It may be because they're relying entirely on GPS, and I don't have the built in GPS activated (I use an external device for Tom Tom on the phone). Perhaps, unlike Google Latitude, they will not attempt to use cell tower triangulation if GPS is not available. However, the ring option worked great. I'm not brave enough to test the other two.