Originally Posted by
bocastephen
Is that for an Android phone, or online? I don't see any menu options for my iPhone
Is your app up to date?
In Google Voice iOS app, it's under settings/make and receive calls; Prefer WiFi and mobile data. There's probably other settings on google.com/voice you might want to check.
I'm pretty sure I've made calls using both the iOS hangouts app and the Google Voice app over WiFi.
-David