I want to use any free SMS service to send the SMS (free) from my application. I am developing the application in C# + asp.net. How can I do the code for that.
It depends where you are based. SMS is likely to be a country specific thing, and thus an telco provided thing, and ultimately they're not likely to be free as the telecos make tonnes of cash from SMS. Even if you find a free service (there seems to be a lot in Western Europe) you contend with the service provider not providing an API or if you resort to screen scraping it will likely be against the sites' usage policies.