A friend of mine has brought my attention to the Google Calendar SMS notification service; Zain and Wataniya subscribers can have their calendar events and reminders sent straight to their phones for free! (Note that Zain is not mentioned on Google’s list of supported carriers, but it works nontheless).
To set this up, simply log in to your account, go to Settings, enter your phone details in Mobile Setup and you should receive a verification code shortly after. Once your number has been verified, you can specify which calendars or events you’d like to be notified about.
The best part of all of this is that since you can share calendars with other google users, people can see your free/busy hours, pick a suitable time for an event and have the details sent directly to your phone. You’ll never miss an appointment again! :)