2.1 Backgrounds about SIP Trunks
The SIP Trunks serve connecting PrivateServer to a local PBX or to a SIP Voice provider. The above statement implies that a Trunk can be used both for receiving and placing calls in a bidirectional way.
The PrivateServer is designed to perform always as a client when configuring a SIP Trunk. This means that PrivateServer itself can not act as a Trunk Provider.
Even if a SIP Trunk can receive and place calls PrivateServer has to be configured to act in a bidirectional way. The Trunk setup should be done for the incoming calls first and after this function is enabled you can setup it for outgoing calls as well.
The incoming calls Trunks are configured in the Inbound entry that you access under Main Menu -> PBX INTEGRATION. Outgoing calls are configured into the Outbound entry that is under the Inbound one.