The web itself is a dynamic "thing" and there are many more "things" designed everyday to connect to the interwebs in the future.
Your website needs to respond to the screensize of the device that connects to it, at a minimum. Your choice is to build a second mobile site (as suggested) or else have the pages on your current site respond to the screen size.
Responsive design for your website is a good thing. It promotes consistency, reliability, and a better experience for users.