A while back, I wrote a post on how to call an Exchange UM voice mail box directly. The trouble with the approach described in that post is that it generates a missed call notification in the Exchange inbox of the recipient. A colleague of mine discovered a way to nix this missed call notification, and I thought I would share it.
You can get a SIP URI that goes directly to a user’s voice mail box by appending ;opaque=app:voicemail to the end of that user’s address of record. For instance, if the user has the SIP URI sip:firstname.lastname@example.org, you can get their voice mail box by calling sip:email@example.com;opaque=app:voicemail. However, this will lead to a missed call notification.
If you instead call sip:firstname.lastname@example.org;opaque=app:voicemail;local-resource-path=voicememo, you will get the user’s voice mail box but there will be no missed call notification.