Skype uses P2P technology to allow users to make free telephone calls, and was co-developed by the creator of Kazaa, Niklas Zennstrom.

From the web site…

“PocketSkype™ is free software that enables you to make Skype voice calls using your WiFi-enabled Microsoft PocketPC based handheld computer from any WiFi hotspot.”

Skype - Getting Started With PocketSkype