Thought you might be interested. I recently found a way to do viop for free. If you have an android phone you can download Google Voice. After signing up you need to download Groove IP Lite (free) or Groove IP (small charge). Once you are set up you can make free viop calls over WIFI with Lite or over WIFI or 3G, 4G with the paid groove IP. I read you can transfer an existing # but I haven’t tried it...
I use nettalk. Device plugs into my wireless router and works with my standard phones. Not need to have computer on, and did transfer existing number.