Sending free SMS in India is now not a new thing using web interface but to send free SMS you have to sign up for an account and every time you have login. Some users do not like this so they want to send free SMS without opening an account. I also have listened there are some services that let you send free SMS without login or signup.
I searched the web for sites that can full fill the wish but I found only two sites, I have already mentioned previously.
This site let you send long SMS, and it is the only website that let you send maximum characters (500) in SMS. All you can do without login but you need capcha.
SeaSMS let you send MMS in India but you can send SMS too. without login. It does not ask capcha that is a very nice thing. You can compose SMS in Hindi language.
This one is in this list, you can send unlimited numbers of free SMS in all India of 160 characters. And it will not include any ads. I tested this service and it worked but sometimes it can take some time to deliver message to check if something illegal.