Hello, you don't have to wait for Sprint to come out with wifi calling on your phone. Wifi calling uses Google Voice. I have a Moto X and i downloaded GV. As I set it up I found that GV has a link in it for Sprint wifi calling. However, I have a lot of experience with this app. GV has a lot of issues. You need to download it anyway. You will need the GV phone number. I found a better way to use wifi calling. Go to your app store and download Google Hangouts Dialer. This app uses GV's phone number and works so much better. Hangouts makes wifi phone calls, texts, e-mail and video calls. This app works well for me. Give it a try and see. Make sure you set up the Sprint wifi calling up in GV first. i hope that this helps!
Yes I have been using hangouts dialer with my own phone number as well as making and receiving calls. This app works for me very well. Since this app runs over the internet there will be a small delay. Too much traffic on the internet. But it can be minimized.