Use ?id= to open a url

[hashsaz]

It might be a funny question, but I hope the pro can help me.

 

I want to use ?id= to display the other page/url instead of showing the full address due to certain reasons.

 

What do I mean is like there are 2 different static page e.g. main.php and subpage.php

 

I would like to use id to display as the url for subpage.php  i.e. main.php?id=1 actually is displaying subpage.php

 

Any idea?? Help!! Thanks!