We have several Zulu desktop clients working on a LAN, some of them working via VPN, and it works fine.
But I wonder if it’s possible to use Zulu mobile on iOS or Android, via LAN, connected to the company’s WIFI.
If the LAN IP of the PBX is used, we get a certificate error on Zulu mobile. Is there any posibility to use it? We are not interested on opening ports to the world.
You can, but Zulu mobile is deprecated now, you should be using Sangoma Connect mobile. With connect, you can define the FQDN/ip you want to phone to register to.