I had a very interesting meeting today at EPFL with Philippe Rochat, a computer science phD student who showed us his SMS game. The game in itself is not that intersting but it was a way for me to understand how it works.
In this game, the cell phone is used as a remote control, results are seen on a screen.
When the user send a sms (players interact with the games thanks to sms), it goes to the telecom provider (say orange), then to a sms gateway, like kannel. The gateway send a url-like line to the server. Afterwards, a php-script parse this line and transfer the result to the interface (java for instance) displayed on a screen.
One can imagine very smart app with this setting. For example, cell phone can be used as a way to ask a question to a lecturer (questions could be displayed on a large electronic whiteboard) or to answer to classroom quizzes.