Philips has announced that sometime next year, a US cellphone carrier will be using its Nexperia 6120 chipset to allow you to make calls on home WiFi networks—for a flat rate of a few dollars a month. Already in the Samsung SGH-T709 phone, the UMA solution uses Philips' BGW211 802.11g WLAN chipset and allows you to go from a WiFi access point through the Internet and onto a cellular network. Carriers can then track those calls with their billing system and move them along to their destination.
Though Philips is keeping mum about a partner in the cellular world right now, the Samsung T709 shown at CES did have options to connect to T-Mobile Hotspots and home networks—so one never knows.
Also announced by Philips was a DTM (dual transfer mode) solution, which would allow simultaneous voice and data transfer over EDGE networks. However, since real 3G isn't something we're getting here in the US yet, we won't worry ourselves over this too much.
Cell Phones to Make WiFi Calls [PC Magazine]