Microsoft Teams - Cannot Assign Phone Number (User Hosted On-Premises Skype for Business)

Overview

When attempting to assign a phone number to a user in the Microsoft Teams Admin Center, you may encounter the following error:

“The user is hosted in an on-premises deployment of Skype for Business Server. This user's number must be changed in the on-premises environment and then synchronized to the cloud.”

This error indicates that the user still has legacy Skype for Business on-premises attributes, even if the Skype for Business Server environment has already been decommissioned.

Applies To

• Microsoft Teams Admin Center

• Skype for Business Server (legacy or decommissioned)

• Hybrid identity (Azure AD Connect) environments

• Teams Direct Routing / Operator Connect

Cause

This issue occurs when:

• The user was previously homed on on-prem Skype for Business Server

• Legacy attributes still exist in Active Directory, such as:    

  • msRTCSIP-DeploymentLocator

  • msRTCSIP-Line

  • msRTCSIP-PrimaryUserAddress

• Teams interprets the user as still being on-prem hosted

• Number assignment in Teams is blocked by design

Resolution

Option 1 – Clear On-Prem Skype Attributes (Recommended when SfB is decommissioned) ✅

If the Skype for Business Server environment no longer exists, you must remove the legacy SfB attributes from Active Directory.

Steps

1. Open Active Directory PowerShell (with RSAT tools)

2. Run the following to clear Skype attributes:

3. PowerShell

   Set-ADUser -Identity user@domain.com -Clear `
   msRTCSIP-DeploymentLocator,
   msRTCSIP-Line,
   msRTCSIP-PrimaryUserAddress,
   msRTCSIP-UserEnabled

4. Force an Azure AD sync:

   Start-ADSyncSyncCycle -PolicyType Delta

5. Wait for sync to complete (typically a few minutes)

6. Validate user is now cloud-managed:

   pGet-CsOnlineUser -Identity user@domain.com | Select HostingProvider

Expected result:

sipfed.online.lync.com

1. Assign the phone number using:

   • Teams Admin Center

   • PowerShell

   • CallTower Connect

✅ Use this option when:

• Skype for Business Server has been fully removed

• No hybrid voice remains

• You want to fully manage users in Teams

Option 2 – Move User to Teams (Hybrid Still in Place)

If SfB hybrid still exists:

Move-CsUser -Identity user@domain.com -Target sipfed.online.lync.com

Then assign the number in Teams once the move is complete.

Option 3 – Modify Number On-Prem (If SfB Still Active)

If the on-prem SfB server is still in use:

Set-CsUser -Identity user@domain.com -LineURI "tel:+15551234567"

Allow time for Azure AD Connect sync.

Validation

After remediation, verify:

• User no longer shows the error banner in Teams Admin Center

• Phone number assignment succeeds

• HostingProvider = sipfed.online.lync.com

• Enterprise Voice can be enabled

Common Indicators of This Issue

• Red banner referencing on-premises deployment

• Phone number assignment fails in TAC

• User previously existed in SfB on-prem

• Migration completed, but cleanup not performed

• Skype attributes still present in AD

Additional Notes

• This is one of the most common post-migration cleanup issues

• Clearing attributes is safe once SfB is fully decommissioned

• Azure AD Connect must complete before changes take effect

• CallTower Connect and Teams Admin Center require the user to be cloud-homed

Summary

This issue occurs when legacy Skype for Business attributes remain in Active Directory.

👉 The most common fix (and recommended default) is to remove those attributes, sync to Azure AD, and then assign the number in Teams.