I have three IP Office 500V2 R9 Essential Edition systems. They are all connected via WAN links. My customer would like to connect them to allow for direct extension calling between the sites. From what I read, it looks like an SCN configuration would accomplish this. When I purchased these systems I added the four port voice networking licenses to each of the systems just in case they asked for this. I have voicemail pro on one of the systems, but I use embedded VM on the two remote ones. Do I have to use the VM Pro for all the extensions at the remote sites or can I continue to use the embedded VM after the SCN is set up? Also, the documentation states that all the extensions need to be unique. For all the sites, if they are all in the 1700s and none of them are duplicates, is that unique enough?