I have not yet been able to find a perfect free SMS website myself, a few which claim that they do are ..
1. Yahoo messenger : you can send a few free SMS and then unless the reciver replyes back to the same number, you cannot send any more SMS to him.
2. Rediff.com Messenger : Same story with rediff.
3. SMS.ac : They allow you to send a fixed amount of free SMS every day.
4. smsjunction.com : Not reviewed.
5. vyomworld.com/sms/ : Crap.
6. Krify : Crap.

Address :