You can't do this without a 3rd party, unless your PC has a SIM card built in. And you simply aren't going to find a completely free party for this, since sending SMS messages costs money. I don't think anyone is willing to give away money like that. Perhaps you don't have to pay but you still end up "paying" by looking at a lot and a lot of ads, and probably also ads inside the SMS messages.
Most SMS services can be addressed via a "magic email address", which usually is something like "firstname.lastname@example.org". Just send a 1-line email of 140 characters or less to that address from the PC. Works great.
The hard part is making it general-purpose. Since the email address varies depending on the receiver's phone service provider, you have either know what that provider's email address conventions are or go through a generic gateway service that can find out and route it for you.
There's a fairly comprehensive list of the email address forms on the Wikipedia, including providers in both the US and in India.
An IDE is no substitute for an Intelligent Developer.