I was recently asked a really good question: how can you disable the “Play on Phone” functionality in Exchange 2007 Unified Messaging? PoP is a handy feature because it lets you use a simple UI in Outlook or OWA to get your voice mail on any phone that your UM server can dial out to. For security reasons, though, some organizations want to prevent people from placing outbound calls to potentially untrusted numbers (like, oh, I don’t know, this).There’s no direct way to do this from the UI, but you can accomplish it with a bit of trickery: set the OutCallsAllowed attribute on the IP gateway used by the UM server (set-UMIPGateway MyUMGateway -OutCallsAllowed $false will do the trick.)
Why does this work? This flag tells the UM server to never send SIP INVITE messages to the gateway for the new call. If there are no gateway objects with the property set to true, then UM will not attempt to place any outbound calls. PoP is the only Exchange UM feature that will result in new outbound SIP INVITE messages; call transfers use the SIP REFER message, so the automated attendant and call answering features will still work. However, this doesn’t disable the PoP user interface, so users will still see the buttons; they just won’t work when clicked.