RE: Mouth calls
Agree with the double reed comments. Make sure you get one that doesn't have any cuts in the reeds though. That adds a degree of difficulty. I would recommend an HS Double D or Raspy Old Hen.
General rule is the more reeds and the more cuts in the reeds the harder they are to blow.
Get one and practice A LOT. It was a year and a half before I was really comfortable with them.
To practice get a CD from one of the call manufacturers, put it in your vehicle and practice while driving. You can listen and practice at the same time and you won't bother anyone while doing it. Another tip is to make a tape or CD of yourself calling then play it back and listen to it. You really don't know how you sound until you have taped it and played it back.