Yes. I do.
Everyone says just use FaceTime, which is great for the iOS eco system. I'm not knocking it. I use it all the time, and it works great. I manage a team of technical folks and it works wonders internationally from any Apple device.
But what about when you want to call someone who uses a non-Apple Device, or, dare I say it, a feature phone? FaceTime won't get you there. Sure you can use a 3rd party app, but that requires installation of software, possibly paying for airtime, dealing with ads, or requiring the other person to have the same app installed.
While it works, it's a crappy experience. You end up with 5 or 6 different voice apps (Hangouts, Skype, Viber, BBM, What's App, FB Messenger, etc.) that you have to keep on your device and then keep track of which of your contacts use each of the above apps. Who wants that? Sure doesn't sound like an elegant user experience to me.
WiFi Calling on iOS 8 beta 3 (only available on the iPhone 5S and T-Mobile) makes all of the the above mess go away.
It's a beautiful solution that embedded in the OS and requires no overhead for apps / storage. Just dial from your contacts on wifi and you are golden. You won't be tied to the iOS ecosystem (not that there's anything wrong with it), and it can be used in places where cell signal is weak.
It also means I no longer need an mCell repeater in my house, which saves me another $20.00 bucks a month.
Lots to like about WiFi calling from where I'm standing....
I've attached some screen shots to show the feature in the latest beta build of iOS 8 b3. Hopefully y'all won't rat me out for possibly violating my TOS for my Developer account.