After performing a flyby of nearby event, the pilot of the vintage amphibious airplane flew the airplane out over a lake near the seabase. While maneuvering, he attempted to contact people on the ground utilizing the common traffic advisory frequency he had heard people using earlier in the week. After failing to reach anyone, the pilot set the flight controls for a slow descent. Then he used his mobile phone to send a text message asking a friend for the radio frequency in use, and upon reply, changed the frequency. After setting the phone down, the pilot looked up as the airplane impacted the surface of the lake. The airplane sustained substantial damage to the front fuselage and hull, left wing, and both sponsons. The pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.