sunspark,
I haven't set one up that way before so I am not sure what would happen, but it seems you get one-way audio.
I have used micollab.domain.suffix where the internal record would go to the MiCollab server, and the external record would go to the MBG. So if I would have it in Teleworker Mode the client would try to go to the MBG which would give one-way audio. Once it goes to the MBG it will try to send the audio out its WAN port as that is where it believes the Teleworker device is at. If I have the router setup to take those internal requests and send them back to the MiCollab then it would work; hairpinning. The problem is that not all routers are capable of this type of service and those that are would require a reset to set them up.
Unfortunately, I have not been working on these too long and have only setup less than a handful of these for Teleworker service, but this is how I picture it working in my head; I could be wrong in that assumption.
Sorry,
TE