Hello, On 31-10 15:21, Peter Hudec wrote: Not behind FW but behind NAT, that's a little bit different. Basically you must make sure that the proxy to which you send the traffic knows how to get responses and further requests back to you through the NAT. Since you don't know that if all the proxies in the wild do support that, you have to choose one and use it as outbound proxy. The outbound proxy will do all the translations for you, even if other proxies do not support that (I assume that you can't modify your NAT and that it doesn't explicitely support SIP). Outbound proxy is nothing special, it is just a regular proxy which receives all your SIP traffic. SER can do this, for example. If you have phones behind NAT than you must also make sure that the proxy has some NAT traversal support. Give a try to our public proxy at iptel.org, it contains NAT traversal features so your phones behind NAT should be able to place and receive calls. Yes, see my previous insertion. Jan.