The WiFi Alliance is now certifying devices for VoIP over WiFi as part of a new standard 802.11r that's coming to us in the future. While this is good, it's too little too late. Earthlink tried to have VoWiFI with some devices that pals David Elgas and Steve Howe actually had built for them. While the handset worked great indoors, when I took the device out for field testing in Philadelphia and Anaheim the service sucked wind, as moving from access point to access point that was powered by the Tropos Mesh networks failed to move between nodes very cleanly, almost always dropping the calls.
This new standard is supposed to fix that, but as much as I see this as good for WiFi in the enterprise, I don't see this working in the metro area for a long time.