SIP@Home is a SIP Proxy server for Windows OS. It allows make calls between SIP devices, such as mobile phone, PC, PSTN. SIP@Home works as traditional SIP proxy server or as full proxy, when all traffic includes voice data goes through SIP@Home. When SIP@Home works in full proxy mode it easy to configure home router to forward voice traffic through NAT, because it is needed to forward only 1 port and you don't need to configure each SIP device, only proxy.