How is my cell phone making calls over wi-fi when I am out away from home? This seems super strange to me. It seems like my cell phone must be connecting to wi-fi without asking me, or having me connect.

Details. I turn off cellular data often on my iphone 6 plus. At home I only keep wifi connected, and have bluetooth and cellular data off. This is to make sure I am using my wi-fi, because my DSL connection is bad and sometimes seems to fail for a few minutes, and I don't want to use my cellular data (that has a cap).

So, I am on iphone 6 Plus. With ATT, in California in a San Francisco suburb (east bay). It's not a city like Oakland or Berkely, but a small town, near Oakland a way away.

Today, I forgot to turn on cellular and drove far away from my home, and I made a call only using wi-fi enabled. How is the phone doing this?. I still get bars when I am away and have cellular turned off. Am I making calls over wi-fi that the phone is finding and connecting? Like some ATT wi-fi network?

Or is the cellular connection on all the time, and the button is only turning off cellular data but not voice? Is that it? When you swipe up and see the options (airplane mode, bluetooth, wi-fi, cellular) is the cellular button only controlling data but not voice?

Maybe that is the answer, but I though for a while it was somehow connecting using wi-fi and letting me make calls away from my home wi-fi.