Try this,
goto
http://www.killsometime.com/TextMessage.asp
here you can send SMS with a from address of your choosing. I like to send msgs and have them look like they are coming from the person i sent them to!
Keep in mind that the carrier can track where the msg really came from and the domain webmaster more than likely keeps logs of what IP sent who what msgs. So its not wise to try to use this service for anything which might be interpreted as questionable.