Ran into an interesting problem tonight that I thought I would pass along. Setting up Voicemail Pro on an SBS 2008 machine. All the licenses etc were correct but I would sporadically lose communications between the IPO and the voice mail system. It ended up being the DNS server grabbing the port 50791 that is used by the two boxes to communicate. I fixed it by adding a ReservedPorts key to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters and putting in 57091. In all my googling I never did find exactly this. I found the problem with debug viewer on the VoiceMail pro machine to see it unable to bind to the port it needs.