They may not be cellular, but Skype was at Unveiled hawking their SkypeIN and SkypeOUT services as well as Wi-Fi phones from Belkin and Netgear.  With a Skype-compatible Wi-Fi phone (or the new Sony Mylo), Skype users can make and receive phone calls over any available WLAN network without the need for a computer. 

The eBay-owned company is set to make a push for your calling business, as their service is cheaper than cellular and land lines, and quickly becoming almost as convenient - particularly in areas heavily blanketed by open wireless networks.