The way the MWI is setup is that it sends an update to the ATA when certain things happen (new message, message deleted, etc). It also sends a periodic update (I believe it's every minute but not 100% sure). The Update MWI button sends an update when you click it.

What would happen if Virtual Numbers were involved would be the ATA getting status updates for multiple numbers that could conflict with it. Example would be if you had a message in the main mailbox, it would send the On signal, but then at the periodic update, the VN box would send the Off signal so the mailboxes would constantly be fighting.

I guess we could structure it so it's a blanket thing where if there's a message in any mailbox on the account it would turn it on looking at all mailboxes as "one", but we thought people may not want that since then there's no way to know if the message i in the real box or the VN box. Since the idea with the VN is to create an independent mailbox separate from the main one a lot of people use them for kids or roommates. So if it got a VM, they would have no way to clear it unless it was a mailbox they accessed too.

Hope that makes sense.