I got an project where I have to create a system like "I will send SMS to a server page in PHP and in return I will get results as SMS from the database". I am familiar with PHP and MySQL, but have no idea how to implement it with SMS system.
Disclaimer, I do developer evangelism part time at Nexmo.
Really, your best bet will be an API that provides sending/receiving SMS. Generally speaking, they all allow you to send an SMS using a HTTP request, and incoming SMS result in a GET/POST (similar to a regular form submission) to a URL you specify.
Here are a few of the bigger SMS APIs: