If it sends an email, you would have to be at your computer anyway... I'm not sure if it's possible with SMS (though it should be), but the main problem there is the cost. Most SMS sites/programs charge you for sending an SMS and also sometimes, place text advertising at the bottom. So I think it's possible, but you'll probably end up paying more than if you employed someone to stare at your monitor and yell when someone comes online
/ 
