Edge Server with internal VPN / single static IP

[Smoothie]

Thanks in advance.

I manage a small network using database services over a VPN firewall router. Currently we only have a single static WAN IP from our ISP. We are adding a VOIP system which will use and Edge Server and VLAN. This will be installed between my LAN and the ISPs modem. They are suggesting that by using a DMZ I won't have to get another static WAN IP. Is this the case and if so how does this work? I have not set up DMZ for this use before. Sounds to me like they are suggesting the Edge server and my VPN router will be sharing the same static IP.

Regards,

Chris

[Smoothie]

Nobody?