Re: Dreaming of the future that could have happend years ago
Voice over TCP/IP will always remain a hack that I believe even skype only uses as a last resort. However Voice over UDP/IP using RTP is extremely common and becoming the standard means for fixed line phone calls around the world.
Support on actual fixed phones has been very slow taking off with most people going through a local gateway (Analog Telephone Adapter). Support from mobile devices is also a little hit and miss, generally using a customised app from your carrier of choice. Free VOIP apps tend to be difficult to configure and lacking in useful features although the situation is improving.
As for roaming between WiFi networks there are a lot more problems than the initial captive portal (a legal necessity as you seemed to party acknowledge) to solve. The change in IP address would be a much more difficult problem to solve.
Even within single organisations with handoff between WiFi cells with the same SSID (and therefore no new captive portal or IP address), the problem of dropped audio within a fraction of a second is still a problem that WiFi vendors are solving with incredible proprietary hacks. Add to that the fact that most WiFi devices resist handoff for as long as possible, degrading performance unnecessarily, don't look to WiFi in the near future to make this work.