How to add a private ip in fortigate 80C and also create a vpn from a sip trunk provider

[Vernon76]

Hi all,

I want to at a direct ip in the firewall from a sip trunk provider  example 156.243.55.22, rtp 20000- 30000 for a pbx.

For what I see in the firewall that the internal network is in the 172.xx.xx.xx range and connected to an ISP.

How can I add Sip trunk provider ip in the firewall, so it can be route to the device it needs to go.

Also if needed how can I create a VPN tunnel directly with the sip trunk provider?

Krs