The data usage incurred by your smart phone connected to the WiFi on your Rogers Internet connection will be part of data usage for whatever means you use to connect to the Internet. Therefore your phone data plan will not be affected by any data transfers done by WiFi. This is an incentive to connect to WiFi with your smart phone whenever you can.
If you use a cable modem, with minimum data usage plans of 20 - 30 Gbyte a month, for example, this will be a trivial amount. If you use a RocketHub (as we do) with a 3 Gbyte a month usage plan, this could be more of an issue. My wife uses an Android smart phone and her phone connects to our home WiFi when she is there, for the reasons I stated above.
I should of made myself clearer. What I meant to say is that when using Wi-Fi, it will not affect whatever Internet data plan you have on your phone. As skinorth has so clearly pointed out, if you use your home Wi-Fi, it will of course count towards usage on your home Internet plan.