As an example, when configuring your TPControl settings for sip2sip.info, use the following Settings in TPControl:
SIP Server: sip2sip.info
SIP Proxy: sip2sip.info
Connection Type: TCP
Outbound Proxy: Enabled
Specifically for testing with AMX devices, as they do not support cross-domain SIP calling nor will they register to web-based SIP servers, I use a local Asterisk PBX server running in a VM when testing AMX devices, using relevant UDP or TCP connection type as configured in the Asterisk server.
We are not restricted in our implementation for cross-domain or web-based SIP registration, hence the reference to the online SIP2SIP service, and we also support SIP Video whereas AMX devices currently do not.