The email-to-SMS trick makes me feel very nostalgic. I still think that was the most brilliant idea for mobile notifications in those days.

Sometime in 2007, I setup a forwarding rule in my GMail account for my long-distance friend's address. When she mailed, I would get it as an SMS on phone and run back home to chat if I was out.

It stopped working after sometime. I'm not sure what happened. I remember reading it was made an enterprise-only service by some telecom operators. If they the service back up and running, I'm sure there are many ideas waiting to be built on top of it.