Please confirm that you have changed UDP Listen Port from 5060 to something else, e.g. 5678. That's the local port number used by the device and can be anything. On a softphone it's usually just whatever the OS assigns.
In addition, use an alternate proxy port (and registrar port) that VoIP.ms supports, either 5080 or 42872.
Also, what is the value of Reg Expire Timer? If it's long, try setting 60000 milliseconds.
If needed, I'll help with setting up Wireshark captures and/or interpreting the results. But first, you need to get the PC to "see" the packets to be captured. One way to do this is to get the packets to pass through the PC, using Internet Connection Sharing or Bridge Connections. Of course, this requires that the PC have two NICs, one connected to the Internet and one connected to the ATA. The other way involves a dumb hub, e.g. an old 10Mbps one, or a managed switch, allowing the PC to snoop the traffic.