[RESOLVED] Microsoft MFA SMS messages not being received

Microsoft posted an update to their advisory indicating service has been restored:

Status
Service Restored

More info: Users were recommended to use voice calls or non-telecom authentication methods to complete Multi-Factor Authentication.

Final status: We’ve confirmed with the 3rd party cellular provider in the United States that impact has been mitigated.

Scope of impact: Impact was specific to users who were subscribers of the impacted 3rd party cellular provider.

[INPROGRESS] Microsoft MFA SMS messages not being received

Microsoft has just posted an advisory:
Details

Title: Users are not receiving Multi-Factor Authentication (MFA) Short Message Service (SMS) messages to access M365 services

User Impact: Users are not receiving Multi-Factor Authentication (MFA) Short Message Service (SMS) messages to access M365 services.

CTS will continue to monitor the situation and post updates when they become available.

Microsoft 365 Additional Security Verification Methods for use of the Self-Service Password Reset Portal

  1. On the “More information required” page click “Next” 
  1. On the “don’t lose access to your account!” page, please set up a minimum of TWO additional verification methods. It may prompt you to configure Alternate Email, Txt (Mobile Phone), Call (Mobile Phone), Office Phone, Security Questions. If you do not set up at least two methods, you will not be able to use the Self-Service Password Reset (SSRP) Portal.  Once you are done with setting up the additional verification methods, please click “finish”.