With the rise of smartphone fewer people are using SMS notifications in favor of native notifications on their smartphones. But for those of you that don't have a smartphone but want to check your Google Calendar on the go SMS Notifications are still available from Google.
To enable them go to your Google Calendar and go to the settings. Under the Mobile Setup tab you can enter your phone number and Google will send you a verification code. Enter the code to verify your number and then you will be able to use your phone to check and add events to your google calendar.