Each PrivateServer can reach outer communication devices using its Trunk feature. This means that it's possible to connect PrivateServer to almost anything out there, if that device talks standards protocols as SIP. The outer communication design can be:
There is some pre-requisite to be filled in before we even start configuring. The most important one is the network connection.
It can sound awful or just pedantic, but it's necessary that both the devices (ie PrivateServer and the other one) can "see" each other, and not just in matters of ICMP Pings, but actually via UDP connection. This because the UDP connection will be the transport mean for the SIP Trunk.
2.1 Number Plan
Also this pre-requisite is often disattended or considered of less importance. This attitude is wrong, because without a clear and stated number plan we can really risk number overlapping which would lead to unexpected call routings and very nasty to debug issues. So please before you start just write down the telephone numbers you are providing to the PrivateServer device to be called and consider the impact of calling secure numbers on your own PBX.