Train as you fight. One handed calling is to me, superior as it becomes a habit and when you sit down to actually call to a Gobbler, your hand movement is minimized. I find that I am more prepared to kill a bird if my gun is on my shoulder and knee. Use your trigger hand to steady the gun and your weak hand to control the trumpet. With practice, it becomes second nature to set up in this manner. One handed calling isn't the only way to run a trumpet, but for a hunter, I really think it is the best way to use a trumpet. Confidence in your calling and technique is the goal.
There has been some good tips written and photos that show the basics... Practice, practice, practice.... It will reward you with dead Gobblers.
Good luck to all.
AG