That's the same question I would ask, brownbecky6!. We also have wireless internet in my home (though with a different residential service provider as FiOS is not available in my area). I have my wife and son’s smartphones programmed to connect to it automatically when they leave. When I noticed a spike in usage on my wife’s line, I asked her if she had changed anything (such as disable Wi-Fi access). She said she hadn’t. I came to realize that the device was still connecting to Verizon’s cellular network even though she was at home and within range of Wi-Fi.
It does that because the device is designed to seek the Verizon Wireless network before other networks. In order to be exclusively using Wi-Fi, one must disable cellular data on the device. To do that on the iPhone 5s, go to Settings> Cellular> turn Cellular Data to “Off”.
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