Yes
Assuming you are using a normal internet connection (Dynamic IP) you need a domain name. The easiest way is register with someone like No-Ip.com or Dyndns.org.
Once you are registered, let’s say with the name (axon.dyndns.org) now pointing to your current public IP you need to set up an external line. Give it a name (anything will do) then an ID Lets say (1000) and a password for safety.
Set the line to ring the extension you want the calls to go let’s say (100) then tick the “Other device will contact us”.
Now when a caller contacts 1000@axon.dyndns.org extension 100 will ring and can take the call.
Don’t for get to forwards Ports 5060 and 8000-8499 from your router to the server private IP if you are behind a router.