The pilot thought he had lowered the landing gear at the final approach fix, but "did not check it down and locked." The airplane was traveling faster than normal as it crossed over the runway threshold and it ballooned during the landing flare. The pilot heard the audible gear warning say "check gear" as he was reaching to increase the throttle for a go-around. The pilot was reaching for the landing gear handle as the airplane settled onto the runway. The airplane slid about 850 feet before coming to rest. The lower fuselage skin and its corresponding substructure were damaged during the wheels-up landing. The pilot said the accident could have been prevented if he had verified the position of the landing gear prior to landing. He also said that he was distracted during the approach with changing radio frequencies, and correcting for being high and fast on the approach.