If I interpret you correctly, you are assuming that you can make phone calls through wifi. The only way to do that is with a third party voip service or something like Skype. Your phone doesn't make regular calls through wifi.
Oh sorry, I mean using my phone to make a call. From what i was told Wifi calling goes through the Internet instead of Rogers network. So I'm assuming I shouldn't be charged. If someone can please verify if I am understanding this correctly. Thanks