NOTICE! This is NOT a Microsoft supported configuration! If this does not work or causes other issues in your environment I am not responsible, and Microsoft will likely not provide support.
First a shout out to my colleague Clayton Martin who helped me figure this out, you can follow him on Twitter @claytonjmartin.
The Scenario
You have Skype for Business or Lync On-Premises with enterprise voice deployed. You have Azure AD Connect setup and you may or may not already be using some Office 365 or Azure services. Now for some use case “I can’t imagine what” or for testing purposes you would like to enable Microsoft Teams Voice for the same user(s) that have SfB or Lync enabled On-Premises.
If you try to just license the users and enable Teams Voice without following these steps the users will not show up in the Teams or Skype for Business admin Portal and the dial pad will also not show in the Teams client. To enable the users online we need to trick Office 365 into thinking the user is homed online, to do that we will edit an Azure AD Connect rule to modify the user attributes in Azure AD.
Editing Azure AD Connect Rule
- On the server running Azure AD Connect open the start menu and search for “Synchronization Rules Editor” right click and run as administrator.
2. Select “In from AD – User Lync” Rule, then click Edit.
3. You cannot edit default rules so you will get a prompt to disable the default rule and create an editable copy, select “Yes”.
4.In the new rule change the Precedence to 99, if you have other custom rules just make sure this number is lower than any other rules that may affect these attributes. Optionally you can change the name of the rule as and apply a scoping filter as well.
5. Select the “Transformations” tab on the left then find the target attribute labeled “msRTCSIP-DeploymentLocator”. Change the FlowType to “Constant” and set the source to “sipfed.online.lync.com”.
Save the synchronization rule and now just wait for Azure AD Connect to run, or in PowerShell force a full synchronization by running “Start-ADSyncSyncCycle -PolicyType initial” on the server running Azure AD connect. Once Azure AD Connect runs it will update the Azure AD user attributes tricking Office 365 into thinking that the users are homed online. Note that nothing is being updated or changed in your On-Premises environment or local AD so you should see no negative affects there, it is just updating Azure AD online attributes to enable Enterprise voice online. This method can also be used for doing a cut-over migration from Lync or SfB on-Premises to Teams Voice.