A student of mine recently mentioned that she wished there was a free service that would make calls to her cellphone to remind her of upcoming events or commitments and even serve as a wake-up call service for her. This prompted me to look around the Internet to see what I could find. Here is what I turned up in my quick searching.
Telepixie will call you with reminders for free as long as you are willing to listen to a brief commercial. If you pay a "small" fee they will remove the commercials and just call with the reminder. They say that they will call your "regular" phone so I don't know if that means they don't call mobile phones. It would be worth checking on before you got to far with this particular service.
Snoozeter is similar but is a fee-based system only. It seems a bit more focused on the wake-up call aspect of things and even allows you to snooze with your cellphone so you can get a few extra minutes of shut eye. I'm not sure why you couldn't just use an alarm clock for this.
If you use Outlook to maintain a calendar you can download the free Outlook Reminder plugin to automate calls to your cellphone with reminders of events from your calendar. You can get reminders e-mailed to your phone from iCal if you are on a Mac and use that calendar tool. Google Calendar also allows for reminders to be sent to your phone but neither Google Calendar nor iCal actually call your phone.
I'm curious to know what other tools people use for this type of thing.