Is this possible? I'm trying to play nice in the sandbox with a phone vendor

Here is the setup: I have a Balance 20x in a small medical practice. I have a business circuit as my WAN ISP, its bridged, as I can see and manage it via IC2. I share rackspace w/ an IP phone vendor who has a dedicated circuit for his phone system. We wants to be able to use my router as a failover for his system. I created a VLAN for him, and it works well in this role. However it is problematic for him as he receives a private DCHP address over the VLAN, he wants to have a static IP so he can remotely access his gear during failover. Right now - he can’t manage his gear when he’s failed over to my network. I think we used to do this with DDNS to get behind the firewall right? How would you try to accommodate this? Is it even doable?

You would need a routed subnet to do this, or you could do it through FusionHub with some slightly advanced configuration. Else, a second modem connected such as a MAX Adapter or 5G Adapter, and set outbound policy and passthrough (or 1:1 NAT).