At some point, your dog might be too far away to hear your voice (especially if you have a small, girly voice like me!).@ Shelby - I just get visions of me going all Captain Von Trapp whistling at my dog. LOL. Why not just use your voice?
We used a lot of voice in the beginning - lots of encouraging - because when they are really young and just starting, it's NOT always built in. They might go running out after the bumper or bird, and then take off and want you to chase. That's where the long line and lots of encouraging calls in help. Once your dog is off the long line and coming in (it doesn't take long), you can start a whistle, but you don't NEED to. You can definitely do a JH and WC without a whistle, but I find it's good to start getting them used to the whistle recall for later handling use. I started to use the whistle for recall a few months before I was going to start teaching whistle sits.