I do not have Voxbeam so I cannot give you any direct help but I can imagine that you have to go to the Voxbeam DID management portal and set it up there properly.
Thanks for commenting. I talked to Voxbeam, and apparently all I needed to
1) Forward the appropriate ports: also discussed here:
https://www.obitalk.com/forum/index.php?topic=4250.0 2) Setup my public ip in the Voxbeam account
And it was magic.