From the Google Earth blog:
Franz Graf knew he had a shaky mobile connection on his daily commute, but wanted to see just how bad it was. To find out, he wrote an Android app that recorded the GPS position and signal strength along his journey and then plotted all of the data in Google Earth. The result is a great Google Earth KML that shows cell tower strength in his area:
The image above was created with approximately 9,000 data points from his commute. He plans to release the app to Google Play so that others can use it, which I would love to download to drive around my area and see how it does. I have some idea of where the dead zones are, but this would give me a more concrete look at it.
He's released a sample KML file so you can see first-hand how the output looks.
You can read more in his original post on Google+, and then the follow-up post where he plotted it in Google Earth. If he releases the app for others to download, we'll certainly let you know about it.