I just got a US Cellular cell phone. They have a service you can pay extra for that gives you an email address that forwards emails as SMS messages to your phone. However, you can easily roll your own using their web SMS sending form. I wrote a script to send messages via that form. Then I wrote a procmail recipe to forward any messages with the subject "SMS":

:0
* ^Subject: SMS
| ~bethenco/bin/usc-sms --email 6084388810

There you have it! Email to SMS forwarding for free.

Feel free to test this out by sending me an email with the subject "SMS"; I get a little thrill every time this system works. I won't reply, though, as I have to pay to send SMS messages.