If I want to have a record in one of the enum.org type lists. Does this require that I have both “Allow SIP Guests” and “Allow Anonymous Inbound SIP Calls” enabled? I tested calling my system and the only configuration that seems to work is both allowed. In E164.org, I have it set to call SIP:@.
That is the nature of enum, you will need to rely on your firewall and careful choice of ports to secure the system.
Some SIP providers (like voip.ms) will give you a sip uri you can use to receive sip calls over a normal registered trunk. Not free, but very cheap and fewer security issues.