"WLAN 802.11 b/g 2.4 Ghz for UMA, with automatic switching between WLAN and cellular networks "

"UMA is the 3rd Generation Partnership Project (3GPP) global standard for subscriber access to mobile circuit, packet and IMS-based services over any IP-based access network, including the Internet. With UMA, mobile operators can now leverage the cost and performance advantages of IP access technologies (DSL, Cable, Wi-Fi...) to deliver high-quality, low-cost mobile voice and data services in the locations where subscribers spend most of their time - the home and office."

More details on UMA today .. http://www.umatoday.com/umaOverview.php

and mobile society blog

http://mobilesociety.typepad.com/mobile_life/2006/02/wireless_voip_d.html