PicoPhone is a Free VOIP Internet Phone application with chat. The author created PicoPhone because most Internet phones use overly complex protocols that can cause problems when used with NAPT routers. PicoPhone uses a simple UDP-based protocol and works well with NAPT. Connections are accepted on UDP port 11676.
Free VOIP Internet Phone - PicoPhone
Authors Website: http://www.vitez.it/picophone
Download: Get this Free Portable VOIP tool HERE