I have a old Samsung Galaxy S2 that isn't on Sprint anymore. It does NOT have any Wifi calling options under settings. I have a google voice number, attached to my main Gmail username, which I use to make outbound calls from my laptop. I have tried the Google Voice app, with and without Sprint integration, but gets stuck trying to "verify number". The problem is I can't receive calls from Google voice web app to verify the transfer. Do you need a cellular connection to make "wifi only" calls? Is it a problem with my phone number? Is the phone too old?