Sip

http://www.transnexus.com/White%20Papers/White%20Papers.htm Transnexus sell some commercial product (something like session authorization / CDR device for asterisk) , but they did performance testing for asterisk (back 2 back sip) and SIP switching for Ser

http://www.voip-info.org/wiki/view/ATS+X10001P DECT sip phone

http://www.securityfocus.com/bid/24560

http://store.voxilla.com/voip-categories/voip-enabled-cell-phones/ Link to a online store that sells Nokia GSM phones with WiFi and SIP client