There are more details at the link below. Two engineers for Edge Wireless had the idea to search cell records for the Kim's phone and contacted authorities with their plan. It took more educated sleuthing after finding the ping (from a text message that had been sent to one of the Kims' phones) and that pointed searchers to the road where the Kim's car had gotten stuck in snow.

http://www.cbsnews.com/stories/2006/12/06/national/main2232874.shtml


Searchers rescued Kati Kim, 30, and her daughters Penelope, 4, and Sabine, 7 months, along a remote forest road Monday afternoon.[color:#000066] The key to finding them, police said, was a "ping" from one of the family's cell phones that helped narrow down their location. Though cell phone signals are rare in the area, reports CBS News correspondent Blackstone, the family's phone connected briefly to a distant tower as it received a text message. That gave searchers a place to look.[/color]