You can still use old devices with WiFi. If you need phone service you can configure a VoIP provider. You lose the cell network but it's still a phone. Some would even say you'd regain privacy this way.
I have tried this in the past with Google Voice. It's just too inconvenient to not be able to make calls when I'm not near a wifi. I've learned that's the #1 feature I value in a phone.
