Starting on January 7, 2019, SMS notifications from Google Calendar will no longer be available. Since Calendar offers in-app notifications, you can still get notified, regardless of your device or connection.
If you had previously been receiving Calendar notifications via SMS, they’ll be replaced with in-app and email notifications. You’ll see these notifications:
As event notifications in a web browser that has Calendar open or a mobile device if you have the Google Calendar app for Android or iOS.
In an email if you had set up SMS notifications for new events, changed events, canceled events, or event responses.
We’ll also be making some changes to the Calendar API to support this change. Check out the Google Developers’ page to learn more.