If I want to use the Skype app for my Wind Nokia 500 AT MY HOME aka my internet connection/wifi - will that be free?
Wi-Fi is a local wireless network. Since Wi-Fi is independent of your plan data any Skype calls or other internet activities made over a Wi-Fi connected network will not count to your total/monthly "data usage".
So if your phone displays the Wi-Fi icon ") ) )" then you can talk all you want over Skype and not care about your mobile data.
Hope this was helpful.