sipXecs wins Miercom / NetworkWorld SMB open source IP PBX test contest against three Asterisk based solutions. To quote NetworkWorld: 

"Pingtel's SIPxchange earns the Clear Choice award for triumphing over the field in our endpoint interoperability and architecture categories. In the latter category we examined how the product was designed to work. SIPxchange comprises some of the more common practices found in larger, proprietary systems, such as direct paths for the media streams. This limits the burden on the server and allows for better scalability and reliability." See the test results here !