[Jake]

... application that runs on BlackBerry, Android and Windows Mobile devices for now. While so many of us focus on throughput, it’s only part of the equation — equally as important is the signal strength, dropped calls, and failed data connections.

Root Wireless aggregates data from the reporting handset clients to create detailed, low-level coverage maps.

Article
http://jkontherun.com/2010/01/15/crowdsourcing-offers-the-best-cellular-coverage-maps-yet/

Company
http://rootwireless.com/products/

Edit: Article is out of date/inaccurate: Root Mobile runs on RIM and Android. Apple and Windows Mobile phones will be supported in future releases.