Starting on June 27th, 2015, SMS notifications from Google Calendar will no longer be sent. SMS notifications launched before smartphones were available. Now, in a world with smartphones and notifications, you can get richer, more reliable experiences on your mobile device, even offline.
Shame because I got use to text messages 30mins ahead of a event as a sign I should go. However they are right, notifications especially since I have the Pebble smartwatch are good enough now.