Ask and ye shall be fulfilled

Speak of the devil. Companies are already starting to offer voice-over-IP-over-WiFi. The service described below doesn’t appear to include the PBX functionality for an enterprise or connections to mobile phones, though:
Pocket Presence and Global IP Sound are working together to build a better-than-PSTN quality softphone application for use in 802.11 connected PDAs and laptops. Global IP Sound said the solution was recently tested on an HP iPAQ device connected by an Wi-Fi connection at an Internet café in San Francisco to another test engineer located in Sweden. Despite traversing 18 router hops, the company described the sound quality as ‘excellent’ and better than mobile and traditional phones.”
(via CANARIE news)