i think many people rely on various forms of notifications from their calendars. google’s calendar supports notification through sms and email. em client can support that too, by just syncing with the googl’e servers. it may not have to send the sms directly. just tell it to the googl’e servers and they will handle all that.
also, multiple reminders for calendar events are a must now days. google’s calendar handles it in the best form today.