I am trying to configure iSip on the iPhone for use with 3CX when I am away from the office. I followed the directions in "Configuring iSip (Connects Apple Iphone) for 3CX Phone System" document. It will not register, it times out. I have enabled port forwarding on my router to forward port TCP port 5060 to the 3CX server. By the way, I also created a profile in iSip to use it internally and it works fine. The only difference in the two profiles (that I can see is the IP address of the domain entry). Any ideas?