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External PSTN Not Available on Cloud Voicemail Auto Attendants in Office 365

Previously, Microsoft announced the retirement of Exchange UM Online and suggested migrating Auto Attendants to Cloud Voicemail.

At this time, Microsoft has not released the feature to allow external PSTN destinations from a Cloud Voicemail auto attendant, and the feature is not expected to be available before Exchange UM Online is retired on Feb 28th, 2020.  As a result, migration of Auto Attendants to Cloud Voicemail for our hosted Skype for Business customers is complicated and requires additional Office 365 licensing.

CallTower has put together several migration scenarios to minimize the impact of Microsoft's UM retirement.

Option 1 - No Auto Attendants

  • If you don't use Auto Attendants, you can keep your user voicemail on Microsoft Cloud Voicemail.

Option 2 - CallTower Hosted Auto Attendants with Users on Cloud Voicemail

  • CallTower will help migrate your Auto Attendants onto our hosted platform, retaining most of the functionality of Auto Attendants in Microsoft Unified Messaging.  Since user voicemail is on a different platform, this option does not support dial-by-name corporate directory in the Auto Attendant.

Option 3- CallTower Hosted Auto Attendants with Users on CallTower Hosted Voicemail

  • CallTower will help migrate both your Auto Attendants and User Voicemail onto our hosted platform.  In this option, dial-by-name corporate directory is supported in Auto Attendants.  Please note that CallTower hosted voicemail for Skype delivers messages as email attachments.  Voicemails cannot be accessed via the Skype client or a Skype handset.


Please contact at, at,  or at 800-347-5444 if you have additional questions.


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