Although Windows' Bluetooth support is a bit weird.
I'm sitting in a hotel room in Canberra, with my old Sony Ericsson HBH-35 Bluetooth headset paired with my laptop, talking to Sarah on her mobile phone, using X-Lite on my laptop, talking to my Asterisk server at home. The call quality is quite acceptable without any QoS.
I should do some maths to work out if the obscene rate the Telstra wireless hot-spot is charging me is less than what it would cost me to use my Australian mobile phone or the hotel phone for the same call.
The next step is to do all of this, but with the iPaq, and on Google Wifi anywhere in Mountain View. Then I'll just have a ridiculously expensive mobile phone.