Microsoft’s Exchange 2007 offering has lots of new unified messaging features and supports PBX integration. It would seem at first that Exchange 2007 should easily integrated with Asterisk. They both run SIP, but soon it becomes apparent that this won’t be easy.

Turns out Exchange 2007 uses SIP over TCP, while Asterisk uses SIP over UDP. There is a solution. By using the open-source tool called SIP Express Router you can convert SIP packets between TCP and UCP so that Asterisk can talk to Exchange and vice versa. Here are the instructions.

Paul Robichaux writes about a similar solution he found for Live Communication Server 2005 and Asterisk:

What is the value of integrating a PBX with Live Communications Server 2005? First, Live Communications Server 2005 is shipping now; you can deploy it without waiting for the Exchange 2007 release. Second, Live Communications Server 2005’s feature set complements Exchange nicely; Exchange provides voicemail integration and a telephone UI for Exchange calendar, contact, and email data (plus faxes and the Global Address List), and Live Communications Server provides presence, IM (including audio and video), and call control. Live Communications Server’s call control features require the software to be able to talk to the PBX so that the software can properly route incoming calls. How do Live Communications Server 2005 and its successor, Office Communications Server 2007, work with Exchange UM? Let’s say that Alice is calling Bob and that Bob’s Active Directory account is provisioned for both a UM-enabled Exchange 2007 mailbox and Live Communications Server. When Alice dials Bob’s number, the following things can happen: 1. If Bob is talking on the phone, the PBX automatically routes Alice’s call to the Exchange UM server. The UM server records a voicemail message, which appears in Bob’s Inbox. 2. If Bob is in the office or working outside the office while connected to the office via VPN, when Alice calls his office phone, Live Communications Server sends a call notification to Microsoft Office Communicator 2005, running on his computer. This notification causes Communicator to generate a pop-up message on Bob’s computer screen using the familiar “toast” window style (like MSN Messenger and Outlook). Bob can use the toast window to take the call on his computer or transfer it elsewhere (such as to a mobile phone). If he transfers the call, Live Communications Server instructs the PBX to perform the transfer. 3. If Bob is feeling antisocial and doesn’t want to take Alice’s call, the phone will keep ringing. Depending on how the PBX is configured, the unanswered call will eventually be transferred to the Exchange UM server so that Alice can leave a voicemail message. One benefit of using Asterisk to enable these scenarios is that it’s inexpensive compared with traditional PBX systems. Even if you buy a preloaded server running Asterisk (and there are many companies that provide such complete, turnkey products), the cost is significantly less than buying a new IP PBX, which in turn results in a lower cost barrier to small-to-midsized businesses that want to deploy UM, enhanced presence, and telephony integration.