Remote extension will not register on port 5070

I have an Asterisk box working just fine. I am trying to get a remote extension connected. Yes, both the phone and the Asterisk box are behind firewalls. Everything works fantastic when I leave the phone on port 5060. No problems, great call quality, etc. I would like to move it to port 5070 tho for a variety of reasons I won’t go into here. I change the phone config to 5070 and changed the sip.conf entry to include a port=5070 for that extension. I can see (tcpdump) traffic but the phone will not register. Yes, I modified the firewalls on both ends to reflect the port change but still nothing.

It’s more than likely a firewall/NAT issue. The easiest way to test this is to bring one phone (or soft phone) to the same local network.