I have had the opportunity to play with the Cisco 7920 Wifi IP phone recently. I have said before I am a fan of Cisco Call Manager (CCM). I use it, I like it. I thought the 7940 wired IP phones were great. This Wifi phone operates just like a 7940 but it is a cordless. I have taken it between 2 locations with the same WEP configuration and it worked seamlessly. I took it between 2 floors with seamless wifi setup and it worked without a problem. The battery life leaves a bit to be desired, and a cradle would be nice for what these things cost, but the phone is still great.
I am tempted to get a wifi IP phone for my personal Broadvoice account. They offer help on configuring them, and they even sell one through Hello Direct. I am just not sure if the quality is as good as the Cisco one? Too bad the 7920 is only a skinny based phone and wont work on SIP.