indeed, this should be done by your service provider... I'm out of my depth with this, I only have an R&D perspective on how this stuff works.
Can I assume you have MCD(s) on your company network, with these UCA "home" users off in the internet? If so, the MBG is setup in your company's DMZ to the internet... But all this is handled by a dealer, it's not something an end customer can install.
I can understand someone wanting to use a VPN to avoid the cost of MBG but VPN's don't work well for voice traffic, MBG is optimized for internet use.