Run sngrep on the PBX and report what, if anything, appears when the extension in Egypt attempts to register. If nothing, check on the WAN interface of your OPNsense. If still nothing, describe the device and network setup at the remote end.
Egypt uses DPI and will block your SIP traffic no matter the port. It might work for a small time, then gets blocked. They can request a special exception from the Ministry of Communications, but VoIP is illegal in Egypt with the exception of in office. Your best bet is to get a VPN that works in Egypt, there are a couple. I have an employee in Cairo and its a bitch getting VoIP to work there, but can be done.
Could you please provide some details? I assume that you tried the obvious (OpenVPN client built into most IP phones with OpenVPN server included with FreePBX Distro) and it did not work, even with nonstandard ports. What issue did that have? Which VPN protocol did you end up using?
By saying “get” rather than “install”, do you mean that a commercial VPN service is required? If so, do you know why that works when the same server installed on the PBX (or at the PBX site) doesn’t? Is the commercial service somehow whitelisted, e.g. because they kick back a percentage to the ISP?
We used a VPN on the front side router before the phones. It’s a bit early in Egypt right now, I’ll ask tomorrow and get back to you as to which we’re using. I know you can google Egypt VPN VoIP and probably find one that works though. Yes - we tried OpenVPN and they know and block it.
Thanks for the update. A search showed solutions using SSTP on port 443. I assume that it will work with a local server and a commercial service is not required. Unfortunately, this or any similar solution involving tunneling RTP over anything TCP based will have voice quality issues if the network has significant packet loss. Do you have choppy voice or other significant impairments?