Jonathan Zdziarski's recently announced AMBER alert iPhone app is now available on the App Store. You can expect to see it on other platforms in the near future as well:
The application helps NCMEC more accurately pinpoint the location of missing children by sending GPS coordinates of your iPhone when you report a sighting. The NCMEC uses the GPS data to coordinate reported sightings and inform the proper law enforcement agencies.
Read more @ Ars Technica.
Read more about Emergency SMS Alert Systems @ Club Texting.