I used my natural voice for 16 years, only manufactured call I ever carried with me over that time was a boat paddle call that I would use to try to strike up a bird later in the day. After my accident that changed, a fall from a treestand left me paralyzed and also left me with about 1/3 of my normal breath capacity and unable to make voice calls. Had to start all over and learn how to use a call.
Greatest compliment I ever got on my natural calling ability was after I made few "voice calls" for a fellow and he said "Man, that's like huntin' over bait."