I always call to him while he is still on the roost if I can. But what I do is to answer him - get the call ready and the instant the gobble stops I give him a soft, 3 note yelp. That is sometimes all it will take to get him to pitch down on my side and come to me. I didn't come up with this idea on my own; it's what I've noticed hens doing many times. I don't think that a soft yelp like this will often scare one, but you never know until you try. What will scare one almost every time is a whole lot of loud cackling and cutting while the gobbler is still roosted. If you can get on the other side of the guy doing that you have a great chance at him.

To not call to him on the roost is also a risk. You run the risk of a turkey that might have been interested choosing instead to fly a couple hundred yards in the wrong direction, and then it might be impossible to get him back.