Another really cool use for SMS...
If you have an AOL instant messenger account, got to http://mobile.aol.com. They have a service which designates your SMS address as the the reciever of AIM messages while you are not logged into AIM. Your name appears as if you are logged in, with a little phone icon next to it. There is a simple on/off checkbox on the web page to turn it on and off.
Even better....you can reply to these SMS messages, and the sender will get it back as if it was sent from an AIM client.
When you log back into AIM, messages are automatically routed to your AIM client. Very cool.