The changes we have introduced relate to the registration campaign feature. For any organization with the state set to Microsoft managed, we are enabling the campaign for users that are fully dependent on PSTN methods (SMS and voice) for their MFA. Those users will then be prompted to start using the Microsoft Authenticator app, a faster and safer way to sign in.
These changes have deployed to most organizations, with the deployment to remaining organizations happening before October 20, 2023. It is possible to exclude users and disable the feature altogether, for which I like you to refer to our public documentation: https://learn.microsoft.com/azure/active-directory/authentication/how-to-mfa-registration-campaign
There are no plans to discontinue SMS and voice.