Windows Phone Thoughts: WiFive: WiFi-based Pocket PC VoIP

"WiFive Phone is the wireless VoIP application that combines the Mobility of a PDA with the Economical Efficiency of IP Telephony service. WiFive Phone lets users make a call to another PDA, PC or PSTN, and allows the service provider to build up a VoIP service platform unifying Wired and Wireless by interworking with wire-based Web Telephony service. WiFive Phone is the best solution that makes up for Handheld Devices' defects by using Polypix's Audio Streaming technology and Optimizing technology. Users can enjoy high-quality Communication service from now on."

Looks like another potentially useful VoIP platform for Pocket PCs. I haven't played much with them, but it seems like the test version is a free download for Pocket PC 2002 and WM2003 devices.