In reality? Probably not, or at least, probably not that last very long...the problem is that phone companies generally charge for SMS messages - so if the company you are using to send them isn't charging you to end them, then it has to get it's money from somewhere.
There is a link to a list here:
http://stackoverflow.com/questions/9344688/free-sms-api-gateway-is-there-any[
^] but to be honest, I think you will endd up with either more hassle (and thus indirect cost) in the long run that you will save in the short term...