^It's already built into the Amaze under the wireless networks settings, it's not longer an app in the app drawer.
Also, for both phones it's required to use the sim card that comes with the phone, as you won't be able to use wifi calling. On the Amaze I got an error saying that my sim card was invalid to utilize wifi calling. So, yeaaah not sure what's so special about the new sim cards, but apparently it matters.