I am happy to say that my service is working now, after a lot of experimentation and help from tech support (they are great). But read on.

Voipo still claims all ports 5004-65000 are needed. What I found works best for me is to put the HT502 on the DMZ port of my router. That enables you to turn back on the advanced firewall features, and you do not need to forward any ports anymore to the HT502. Voipo also said that they "moved" my HT502 to a different server, whatever that means exactly. I also turned off UPNP and am not using any ports in the range 5004-65000 currently. What I don't know is what will happen if some of my other devices will be using any port in the 5004-65000 range. I am planning on turning UPNP back on in a few days, see what happens once I get holes poked into that range of ports.