UMA

aka UnlicensedMobileAccess

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, WiFi...) 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.

Now known as GAN Generic Access Network

http://en.wikipedia.org/wiki/Unlicensed_Mobile_Access

GAN is designed around connecting directly to an existing 2/2.5G GSM network. As such it is only suitable for network operators who have an existing GSM network. For operators such as "3" in the UK this is not the case. To address the issue a development called EGAN is under way in 3GPP.

2010-10-06-TmobileAndroidWifiCalling