According to "Create an event via SMS - Google Calendar Help"...
To create an event on your primary calendar via SMS, simply send a text message containing your event's details to the shortcode "GVENT (48368)."
For example, if you send a message with something like "Shopping with Sarah at Monterey Market 5pm Saturday," Google Calendar can figure out what you mean and pop the new event into your calendar.
For example, if you send a message with something like "Shopping with Sarah at Monterey Market 5pm Saturday," Google Calendar can figure out what you mean and pop the new event into your calendar.