Originally Posted by NJBlackBerry
You never completely escape the carrier. UMA (the voice of WiFi piece) takes your voice call over WiFi and hands it to the carrier. T-Mobile still knows about it and charges you. There is no free voice client (yet) for the BB. AT&T does not support UMA at all.
As far as I could tell if you swithch the browser setting to wi-fi, then the carrier does not know about the data being transferred. The data transfer is between the BB ans the router directly. feel free correct me if I am wrong.