Do you want to send free SMSes(India only)??? Mobile SMS Life is the best thing for this in my view. Earlier 160by2.com was the leader but now it allows only 10 SMSes per day on a single number. SMSLife comes to rescue. It allows 100 text messages and 10 voice messages per day on any number in India.
SMSLife is a java application so it can run on any phone that supports J2ME. You must've GPRS active, for sending messages. Download the app directly into your phone from their mobile site m.smslife.in. You need to register an account on their website before you start sending messages.
The voice message feature is cool. Whatever you type and send, will be read by a female voice in a call to the receiver. The call comes from a number from STD code 044.
Use and enjoy :)