I have just had a thought. Those USB dongles that you can now get from the phone companies. If you could get those without the USB and with Wifi. Now that I’d buy!
The closest I can see to it is Virgin’s broadband modem, but that is plugged in, and has VOIP and all sorts of other things built in.
YOu might be saying at this point, what about the battery size. But I’m sure if there are Wifi phones now, this can be done, and to be honest I don’t think you’d need that much charge. Maybe an hour or two at most until you get to a desk.