When an activity on your Google calendar is about to begin, a text message is sent to your android device.
If
Any event starts
This Trigger fires a set number of minutes before the starting time of any event on your Google Calendar. Note: The time in the ingredient will be based on the timezone set in Google Calendar.
Then
Send an SMS
This Action will send an SMS from your Android device to any phone number you specify.
Explore more great ways to automate Google Calendar and Android SMS