I use my iPhone for Skype voice and video calls all the time.
Fido used to offer a service called FidoUno that used a UMA technology (UMA= Unlicensed Mobile Access). If you had a phone with the same technology (Nokia 6301) you could use a Wi-Fi network connection to make phone calls. The phone would treat the Wi-Fi in exactly the same way it would treat a cell phone radio tower. As far as I know Fido decommissioned their UMA servers.
Just wanted to update this older thread.
Wi-Fi Calling is currently available with iPhone 5c/5s and above with iOS 9.0 or above. It is also available with the following Android phones purchased from Fido:
-LG G4 and LG G5 with Android 6.0 or above
-Samsung Galaxy S6 and Samsung Galaxy S6 Edge with Android 6.0.1 or above
-Samsung Galaxy S7 and Samsung Galaxy S7 edge with Android 6.0.1 or above
It does not work with UMA Hotpsot and TeleTypewrite.
Hope this helps!