I have tried quite a few applications that supposed to send SMS-es for free. None of them quite worked. My sister sent me an invitation to frype.com (frype.lt as well) where it's possible to send SMS for free around the world. I tried to send to Lithuania and Sweden and it worked. It will add an advertisement in the end but you still got a free sms with 160 symbols. I am not sure if this service will last long but if you would like an invitation (they don't do open registration for now), drop me a line.
UPDATE: Frype has changed the rules and free SMS service is not available anymore so there is no real point in opening an account with them.