We currently run a Mitel 5000 phone system and are trying to connect an iPhone using the 3cx phone app. It connects and works internally but i am unable to get it to connect out of office. Do i need to use the 3cx tunnel? The screen just says 'unable to register', 'no tunnel'. I connect using our external IP on port 5090. I have opened port 5090 and port 5060 on the firewall. any help gratefully appreciated.