As of today, both Rogers and Fido offers UMA (Unlicensed Mobile Access). With UMA compatible devices (Rogers is offering so far Nokia 6086 only, no word on Blackberry devices, such as 8320 and Fido is offering Nokia 6301), you can make free calls over Wifi using your phone without using your minutes.
For details, see Rogers and Fido sites.
Rogers calls it "Home Calling Zone", whereas Fido named it "Uno". Both are charging $15 for unlimited local calls or $20 for Canada wide unlimited