You might try this call, it used to work well on the hogs we raised. It goes like this:
Soooweeee, pig, pig, pig. Soooweeee, pig, pig, pig. Soooweeee, pig, pig, pig.
Repeat as necessary until they arrive. Used to not take us anymore than that to have them at the trough to feed.
In case you can't tell I have little use for such things as hog calls. It's just not been my experience that they are prone to come to any call or even to the sound of other hogs in the area. I've observed them a lot and just never noticed the grunts, snorts and other sounds made by hogs attracting others to them. Now the smell of food is a whole nother story and the sound of a feeder going off if they are used to one in the area is like a dinner bell to them for sure.