"Talkatone is the best option for replacing your native phone to call and text for free without using cell minutes. By contrast, Skype, Viber and Facetime are only free if the recipient has also already installed the app. Download the app on App Store or Google play." -https://www.talkatone.com/
A friend needed a phone for making local calls. Budget was non existing, and I only had an older Kyocera Durascout running android 4, but thanks to Talkatone he can now make phone calls wherever he can get wifi now.
I was so impressed with the service that I wanted to share it with the world.
It's available for android or iPhone systems, and it's free.
Not only was it easy to set up, but the call quality was exceptional. He can call any local number as long as he has WiFi access now.
It also comes with free texting, so win win.
Give it a try if you are just trying to save money by not using your cell minutes or cell text services as well.
But for finding a new purpose for "service dead" phones, it's stellar.
-Denny