Wi-Fi, VOIP & Curve

I am looking at the Curve but also considering the Pearl-2. But to me the Wi-Fi feature from T-M on the Curve is a spectacular feature because of the VOIP feature. Does anybody see any chance of other carriers offering Wi-Fi on Curve or other future models ? Or does my desire for that feature force a move to T-Mobile ?

AT&T offers WiFi on the 8820, but they don't have any UMA capabilities. Right now T-Mobile is the only choice for that.