Only problem for me with that is that I use my phone a lot all day. I rely on cell towers for constant coverage. I'm not always around wifi, and I don't want to be tethered to a headset. I want to pick up the phone and answer it.

It is great for people that use VoIP apps a lot though. You don't need to bring your computer to the hotspot to use VoIP.

I wonder if VoIP works on the iPhone over 3G? I'll have to RTFM.