I am somewhat new to Google Calendar. What strikes me is that apparently it can send SMS notifications to mobile phones around the world free of charge (or, at least, I don't see any warning text telling me about charges).
This seems strange to me, especially since many network operators around the world still charge quite a lot for SMS services, and in this manner people could very well use Google calendar to send themselves SMS without paying for them. Then again, with all those internet messageing services available nowadays, who would care to use SMS.
Best Answer
https://support.google.com/calendar/answer/45351?hl=en