I purchased through Google Play. I am with T Mobile which offers Free wifi calling with my plan. The Google version does not have wifi calling. I have read from some that the T Mobile phone does have wifi calling (I have also read that it doesn't.) The feature was not worth the additional $100 for the T Mobile version for me.
I need wifi calling on the rare occasion that I am in the mountains (2 ski trips a year.) There was an app that I purchased that allowed me to wifi call last winter. I had heard that it would be shut down in April.
There was some speculation that it was because a new version of Google voice would allow wifi calling and Google wants us to use that. I will look into it next January.