For each calendar, you can set what notifications you want: pop-up window inside Google Calendar, email, SMS, or a combination of all of these. Just click on the arrow next to each calendar from the left sidebar and select "Notifications", then add up to 5 event reminders. In order to receive SMS messages, you need verify your phone number first.
But if you have special events that require a different kind of reminder, you can set it when you create an event in the Options section.
