Each phone was attached facing out through a window cut into the side of a styrofoam beer cooler, and was set to shoot video and pictures while running SkyMaps. Once launched, the weather balloon would lift it to around 100,000 feet, at which point the balloon bursts, and the cooler tumbles back to Earth slowed by a parachute.
The coolers can land as far as 200 miles from the launch site, so the Google engineers use the phone's GPS to locate them on the ground. So far they have recovered six of the seven launched, and all remained fully intact.
That sounds a lot better than my last cellphone, which failed to survive a one second dip in a sink full of soapy water.