Originally Posted by Need

Don't know about WiFi calling, but with Google Voice, you don't need a SIM card in your phone. What you do need is a valid US mobile number to setup your Google Voice account. You get to choose an US number for your google voice. They require a valid mobile number (non Google Voice) to link to the account because otherwise people will just create throw way phone numbers and use them for telemarketing or scam calls.

My normal mobile number on T-mobile is 909-ABC-CDEF in California. When I was picking my Google Voice number, I saw that I could pick 919-ABC-CDEF in N. Carolina. So now I own both 909 and 919 of the same numbers. That makes it easy to remember my GV number.

I don't know if they let you install Google Voice app on tablet or not, but before when it was Hangout Dialer app, I could install it on my tablet with just WiFi. I could use my tablet like a really huge phone to make calls LOL.