Use Twitter as Alert system
Twitter is a very handy system to send alerts to your friends on mobile,email or Instant Messengers. Twitter API providers an easy way to send your web site related alerts to your subscriber. You don't need to get worried about target system. Twitter subscriber have facility to choose SMS,Email or IM to receive all alerts. What all you would need to give URL of your Twitter Profile for subscription. That's it!
I just found an example of using Twitter in php. Check here