I use my voice, dose'nt do much good.
I also use a gallon can with a hole in the bottom with a shoe string through it. Stuff the can with a hat, and wet the string, and pratice running your fingers lightly over the lenght. If you get good at it you can make it sound like a bull grunt or a cow call.
Everybody knows that the horns work, so this is just about your homemade moose calls.