dan231,
I am not going to comment on what you were sold as I do not know the circumstances of your entire company, but did you have this discussion with your vendor prior to it being installed?
As for the mailbox issue it would depend on how many users you have on whether or not moving the entire company to one VM system is going to work for you. It would also depend on whether it is a good idea on how often your network experiences connectivity issues and how your call flows at the other sites are setup. Do people normally call the "Main Branch Office" to talk to someone at another location or are there no direct numbers associated with those sites; how is the trunking setup? As you can probably imagine there are a few things to think about when setting up a networked system; I assume they are networked that is.
There is another option, that requires the systems to be networked, but you could create some phantoms that forward to one of the users on another node and then create an extension ID for those phantom extensions; did I mention I hate this idea.
This may be something you want to contact your vendor about and have discussions with them as they would have a better idea of what they installed and why.
Thanks,
TE