How can I find a lost phone or help people return it?
Try Prey for Android.

Some features: 


To trigger it, you send an SMS with specific text (default: GO PREY)
Once triggered, starts recording its location to display on your Prey dashboard
If "missing" you can put text messages on the screen or cause a loud alarm to be played


Here's a recent review: http://www.downloadsquad.com/2010/10/28/prey-for-android-is-an-open-source-anti-theft-service/