@Andy_Wismer sorry, yours might be a “non answer”.
@ertank would you please publish a screnshot (in english) of your currently Port forward settings?
Also, i published few months ago a 3CX Windows Installation to internet, solving some issues, but i don’t remember the ports that 3CX needs. Would you please report all ports needed by 3CX into this topic?
NethServer it’s not like pfSense, in various ways. Different source of OS (BSD PfSense, Linux NethServer), different source projects (Hardly tweaked FreeBSD, application enhanced CentOS), different goals (powerful router/Firewall for pfSense, multifunction device for NethServer, also can be a VOIP PBX too) so the tutorial for PfSense may or may not fit completely for NethServer.