We have identified an issue impacting Multi-line (Multiple
Number Assignment) feature for Teams Phone enablement related to the
usage of AlternateId in customer internal implementations for
Azure Communication Services (ACS). AlternateId is an Microsoft internal
usage parameter for phone numbers related to Multi-line in Teams Phone. To
ensure compatibility with the phone system, AlternateId should not be
used by any customer for ACS. We have detected that some customer
configurations are currently using non-phone MRI values for
AlternateId in internal provisioning workflows. This configuration is not
supported and can result in call failures or unintended
behavior as Multi-line capabilities are enabled within your tenant.
Action Required:
If your organization is using AlternateId:
- Ensure that usage of AlternateId is
ceased immediately
- Continued
use of unsupported AlternateId values may result in service disruption.
Temporary Mitigation (If More Time
is Needed):
If you are unable to complete the required remediation
immediately, you may request to be added to a Multi-line feature
blocklist by contacting Microsoft Support.
Being added to this blocklist will temporarily prevent
Multi-line enablement for your tenant while you work to correct your
AlternateId implementation. Important: This blocklist will expire
on June 15, 2026.
If you need assistance with remediation or require temporary
blocklisting, please contact Microsoft Support.