I know it might sound crazy, but there is a difference between "using wifii to send/receive a cell phone call" and "using your cell phone to run an app that makes calls using wifii".
Where I live we don't get cell coverage for either T-mobile or Verizon, but I have a good 20mb internet connection. My wife has T-mobile and I Verizon. She can send and receive calls at home on her cell phone because it switches to the wifii connection. Mine does not. So while I could put Skype or similar software on my cell phone and make calls - people calling my cell phone just gets a voice mail. My wife doesn't have that problem.
Because of this, we've had a landline phone bundled with internet service. It costs like $45 more for having the landline. But no longer. I got a local phone number (same area code and number, only the 3 digit prefix changed) through Skype. Then I put Skype on my desktop, both our cell phones, and both our Kindle Fires. We can answer on whichever device is closest by. Costs like $3 a month for the number and $3 for the unlimited call plan.
Added advantage is my "home number" now is on my phone and can be answered almost anywhere I am. I plan on testing for a couple of weeks then killing the landline number we've had for 30 years. I'm going to try forwarding my cell phone to my Skype number to see if that works next.
Yes, it would be nice though Verizon offered similar service as T-mobile.