The pilot of a Cessna T210M lost control and collided with level terrain, 3 miles south of the airport while on an IFR flight. Radar contact was established with the airplane as it climbed through 300 ft MSL. The radar data indicated the airplane appeared to be established on the assigned heading of 150 deg. After the pilot received Air Traffic Control (ATC) clearance to join the flight plan airway and resume own navigation, the airplane was observed to enter a descending right turn. As the airplane descended through 1,000 ft MSL, ATC attempted to contact the pilot with no response from the pilot. Witnesses on the ground observed the airplane descend out of the overcast in a near vertical attitude. Two witnesses indicated they heard the airplane's engine overhead heading westbound and then turn eastbound. One of the witnesses stated, "The engine sounded normal there was no sputtering or anything." Examination of the airplane wreckage did not reveal any evidence of mechanical failure or malfunction.