HELP| SMS API GATEWAY

Hello :)
Im working with my UnderGraduate Thesis. Is there anyone who can help me with the sms function of my website.

* Receives messages from customer then save it into the database
* Send auto reply for customers

Thanks in Advance :)

Okay, and where's your problem? Please describe here your problem

In order to send and receive SMS from your application you need a SMS gateway. You can either buy a SIM card, plug it into a computer and setup a gateway there or choose one of the thousand SMS gateway providers which are out there... SMS Gateways are NEVER free, but a few are offering their services for no money - in return you are giving away information or contact details to 3rd parties. I would recommend you to search for a SMS gateway service with an easy API (REST/SOAP...) and start developing against it with a testaccount.
Have a look at nexmo.com, havn't tested it but looks promiseful.