SMS => $M$

http://www.textmarks.com/monetize/

This looks like a promising API to get and send sms messages from a
ruby on rails (or other) app.

You can also set up super easy responses like "Send theorybunny to
41411" and have textmark reply to the user with whatever you want it
to say...

a cooking show like cooking with the pan could do this... you could
send "cookwithpan" to 41411 and get a little recipe back.

Man, these possibilities are endless...

Love sms.

Here's more about the textmarks API:
http://paininthetech.com/2008/01/03/integrate-sms-in-your-application-using-textmarks-part-2/