Using MS UM for voicemail

[hchucky]

I am currently running PIAF v1.6 (Asterisk 1.6.1.10, CentOS 5.4, FreePBX 2.5.1.5 (upgrading to 2.6 soon) along with MS Exchange 2010 with Unified Messaging installed. I currently have Asterisk and UM configured and talking to one another in that I can via softphone dial an extension and get the UM Auto Attendant or dial a different extension and get subscriber access.

My question is how can I configure Asterisk so that it uses Exchange UM as its default for voicemail? I have seen examples of how do this but they involve directly editing older versions of the extensions.conf file.

Thanks,
HC