I think the
Linksys EIP300 WiFi VoiP phone would appear to be vendor idependent but don't quote me on it. It is a sip phone and I'm not sure that is what you want as I've heard they can be a bit of a nightmare in internet cafes doing some sort of DNS-redirect-login-screen thing to sign in to their service. I think that Netgear are about to bring out an independant wifi phone as well.
However if you are after a value for money wifi phone Edge-Core do the
WM4201 Wi-Fi Phone for users that are looking for a mobile and easy-to-use IP wifi voip phone. It does however come with skype pre loaded on it.
sorry I couldn't be any more help
