There are many websites that allow you to send free sms messages from your laptop/ computer. However if you wanted to send a sms from your mobile phone then you needed to pay the tariff.
However now you can send free sms messages from your mobile as well. The free sms site http://www.way2sms.com has comeup with a wap version at http://way2sms.com/wap Go to this url through your mobiles browser and send unlimited free sms messages from your mobile phone. Ofcourse you will need gprs connection in your mobile to avail this facility.