How can I make a phone call on Google Voice on a phone without mobile service?

On an Andorid hone without mobile service, I try to use Google Voice to make a phone call in two ways: - is it possible to make a phone call on Google Voice app? It always asks for verifying your own phone number and linking number. - When I try to open voice.google.com on Google Chrome browser, and try to make a phone call, it asks "Google will call your phone and connect you to ...". (I used to have a mobile service, but now don't.) How can I make either way work, without having a mobile service? Thanks.