Cellphones don't offer much shade on a bright day. But in December, Philips Electronics filed a patent on a system that would allow the devices to help prevent sunburns and skin cancer. The plan integrates information about a cellular customer's location with real-time local data about how much ultraviolet radiation—the component of sunlight that can harm skin—is hitting the area, as measured by the National Weather Service or yet-to-be-installed sensors at popular outdoor spots like beaches and ballparks.