I call "Heeeeeeere, chick chick chick chickeeeeeeeees" or "chick chicks" and they all come running! Even if they've snuck onto the neighbor's acreage (which my neighbor is totally cool with) they will come flapping in from all directions. Friends get a kick out of it, they can't believe how friendly my chickens are!
If they see me walking around the yard, they tend to follow me around anyway. I love my chooks!