I would think this is going to be tricky if the phones are connecting via the local ip. Unless your plan is to change the IP of the remote one to the same as the main, in a failover event.I'm planing on using the 15.5 Enterprise license for an active-passive configuration. Both servers will be on the same subnet i.e. 192.168.1.1/24 that will be expanded across the VPN. They will also be registering to a online SIP service.
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.