I am going to need to put my pstn gateway on internal addressing in the near future. I was wondering what solutions are out there for translating the traffic from public to private? A simple static nat using iptables? will that work? Whats out there in the open source world that can function like these 'session border controllers'? My SER box will still exist on the public internet, but for gatway calls I need a way to get my offnet users to this internal ip without creating any port conflicts.