How websites are sending sms to mobile?

[vichu]

Is I own a website, can I send sms from it of free of cost. If no, then clear me yar how webs are sending sms to mobile. Is there any software to buy

[Peter G]

Smaller sites got their webservers connected to a simple Computer that has at least one modem, which actually works just like a normal mobile phone. Bigger sites like twitter are directly connected to the telephone network.
So the the applications on a Webserver get the input from a user or an event triggered by a user and then forward it to the sending computer.

There are no services around the web who have got an API for sending SMS-messages for free. So if you really need this function on your site you have to contact your provider of the webserver. This will by no means be free of charge.

(Sorry for my bad English, this is not my native language.)